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Waste Management — Part 2 Print Email
Being familiar with the various components of a motorhome's waste plumbing systems, and performing regular maintenance, can help owners avoid the "big stink."

By Gary Bunzer
January 2011

Part 1 of this article (December 2010, page 40) discussed drainage lines, venting, and odor control in the waste system. Part 2 will examine holding tanks, additives, valves and terminations, tank monitors, the sewer hose, and more.

Holding Tanks

The sewer hose locks to the motorhome's four-nub bayonet fitting, which could potentially lead to seal damage and leaks.If you own a motorhome, you know about holding tanks. What you may not know is that only the black holding tank is required to have a 3-inch outlet. Liquid (gray) waste tanks can be outfitted with a drain opening as small as 1 1/2 inches. A smaller outlet restricts the flow of waste water as the tank empties. A slower, less forceful drainage flow often will not have enough velocity to totally flush out the tank, the termination assembly, and the sewer hose, which could result in the retention of waste residue. Any accumulation of waste can lead to odors. It should be obvious by now that one of the intended purposes of this two-part article is to eliminate or at least minimize waste system odors, so hats off to motorhome manufacturers who utilize 3-inch outlets on the gray tank as well as the black holding tank.

Tests have proven that faster dumping sequences will increase the flushing action, resulting in all waste being quickly washed away rather than having it slowly recede down the tank walls and trickle through a smaller opening. This negative hydrophilic action is akin to observing buttermilk as it slowly trickles down the sides of a drinking glass.

Many people divide (at least ideologically) RV waste plumbing into two separate systems: the gray (liquid waste) and the black (solid waste). However, in some cases — primarily because of floor plan designs — a motorhome may have one or more liquid fixtures draining into the black holding tank. This is not an optimum situation, because it can necessitate more frequent tank evacuations. While this type of installation is permissible by code, it could put an additional burden on those who prefer dry camping.

Tank Additives

Another odor-related topic motorhomers should consider concerns holding tank additives. Much has been cussed and discussed about products that work and don’t work, but my recommendation is that folks use environmentally friendly additives that do more than simply mask the odor in the tanks and break down solid waste. Enzyme-based, bacteria-infused holding tank additives have become the preferred, and likely the most effective, additives used today. Please note I said “additives,” not chemicals. Enzyme-based blends actually digest the odor-causing molecules at the source inside the waste tanks, thereby eliminating odors rather than masking them. We’ve all smelled so-called additives that were almost as obnoxious as the tank odor itself, right?

Some holding tank treatments may consist of chemicals such as formaldehyde and quaternary-based or phenol-based compounds. The issue of chemical products has prompted many state parks, campgrounds, dump stations, and local municipalities to ban the evacuation of motorhome holding tanks if such chemicals are used.

Motorhome holding tanks are living, thriving environments, to a certain extent. With the inclusion of an enzyme-based, live bacteria additive proliferating and percolating inside each holding tank, never use antibacterial soaps, detergents, or home brews commonly discussed on Internet forums. Such use can destroy the “good bugs” that are more beneficial in helping to eliminate odors.

Tank Monitors

Nearly all motorhomes today feature some visual method of determining the levels in onboard containers such as the fresh water tank, both waste holding tanks, the fuel tanks, and the propane container. It’s a nice convenience to simply push a button inside the motorhome to find out how full the holding tanks are and when it is time to find a dump station before a panic develops.

Some holding tanks are equipped with “through-the-wall” monitoring sensors, while others utilize externally applied electronic sensors. It’s the “through-the-wall” sensors that tend to aggravate owners. False or inaccurate monitor panel indications caused by tank sludge and debris hanging on the sensor probes inside the tank occur far too often. That’s the bad news. The good news is that a revolutionary in-tank sensor for both the gray and black holding tanks has been developed by Horst Dynamics. These new probes are now available and can be installed by any RV handyperson once the original sensors are accessed. To read an expanded product review article about the Horst Miracle Probes, visit

Tank Blockages

The most fearful line item on any RV service technician’s repair order is the one that states, “Black tank plugged; tank is full.” Nothing can ruin both a motorhome owner’s and a service technician’s day faster than having any type of blockage in a holding tank. And, as you might have guessed, it happens predominantly with the black holding tank. This is why most RV service techs keep an extra uniform at the shop at all times.

Unfortunately, some holding tanks are constructed with an offset “shelf” built into its configuration in order to accommodate a specific floor plan. Most toilets are positioned directly over the black tank, and there have been instances when the toilet empties into the tank right above this integral shelf. Mercifully, not many motorhomes are built with this ill-advised design, but there are some out there.

The easiest way to avoid black tank blockages is to use copious amounts of fresh water each time you flush solid waste. Those who completely flush out each holding tank after evacuation will likely avoid the dreaded holding tank blockage. As mentioned in the accompanying “Correct Waste Evacuation Procedures,” be sure to always cover the very bottom of each holding tank with fresh water after each evacuation. And do not store the motorhome for lengthy periods with contents in the tank. Dried-out solids can cake against the termination valve and in the smaller, more restricted, outlet of the tank.

Tank Terminations

All holding tanks, as experienced RVers know, are equipped with a fullway termination valve installed somewhere downstream of the tank outlet and just prior to the termination assembly where the sewer hose is connected. The termination valve (also called the tank valve, dump valve, slide valve, waste valve, blade valve, gate valve) often is improperly installed at the factory. For years it has been a common practice to install the valve(s) in a horizontal orientation whereby the body of the valve is positioned parallel to the ground. In some cases, I have even seen the valve slanted drastically downward. It is my opinion that manufacturers do this to allow for an easier pull on the T-handle when evacuating the tanks. In some cases, it’s to accommodate the installation of those dreaded cable and pull rods. A better installation should have the body of the valve straight up or at least slanted upward. Here’s why.

The larger main housing of any termination valve is simply a void into which the blade can be positioned during the evacuation process. With the valve closed, it’s just an empty cavity. While evacuating a holding tank, if the body of the valve is mounted horizontally or downward, water, waste particles, and tissue residue can easily migrate or literally pour into this void, since the seals on each side of the valve do not close together completely with the valve in the open position. Over time, the valve either fails or begins to leak, allowing seepage when in the closed position and compounding the odor issue. A much better orientation is with the valve body slanted upward, with the optimum position being straight up so that no moisture can enter that cavity in the valve housing.

In some cases, it may be possible to reorient the existing valve to a “body up” position simply by loosening a hose clamp and rotating the fitting. In other cases, new fittings may be necessary. If replacing tank valves seems to have become an annual habit, perhaps it is time to consider revamping the termination assemblies into a better configuration.

Valve Maintenance

Typically, the holding tank termination valves are bolted in place between two adapter fittings using a universal, four-bolt pattern. After one drains and flushes the tanks, the bolts can be removed and the valve detached from the adapter fittings and removed. Each termination valve can then be cleaned, dried, lubricated, and reinstalled. Unless they have physical damage, old seals can be rejuvenated by lubricating them with the same Dow 111 grease suggested in part one of the article for use on the anti-siphon trap vent devices (ASTVD). Small quantities of Dow 111 lubricant may be purchased from Drain Master (

Speaking of Drain Master, I’m a big fan of not having to crouch down in the mud or crawl under the motorhome to awkwardly pull on a T-handle or yank a cable to open the termination valve. Drain Master’s 12-volt-DC electric gate valve simplifies the process of evacuating the holding tanks. With the sewer hose connected, a push of a button will open the Drain Master valve in less than one second.

Sewer Hose

If motorhome waste management is the most disagreeable aspect of the RV lifestyle, then subpar sewer hoses have to be the most aggravating component found in the RV waste management system. And, frankly, I’m a bit perplexed by this. In part one of this article, I mentioned that motorhome makers must adhere to the precepts put forth in NFPA 1192. Likewise, federal, state, and local codes mandate how campground sewer systems are to be installed and maintained. Considering the hygienic ramifications of human waste processing, it’s likely to be one of the most stringent standards in most locales. Yet no standard exists for that crucial link between the motorhome waste outlet and the sewer inlet in any campground. RV owners must find a suitable aftermarket method of transferring waste from the motorhome system to the campground sewer inlet or dump station. It’s my opinion that motorhome manufacturers believe their responsibility ends at the sewer cap, and campgrounds believe their responsibility begins at the sewer inlet. Seemingly, both entities bid us good luck in getting holding tank contents safely from point A to point B. And this is why it’s all too common to find spillage, contamination, and more at some RV sites and dump stations.

Most manufacturers do supply an inexpensive sewer hose with the motorhome, but it’s not uncommon for motorhome owners to have to purchase multiple sewer hoses each year. And many motorhomers have a tendency, time and again, to buy hoses based only on price. Cheap, thin, wire-bound vinyl hoses will develop pinholes over time. I recommend purchasing a quality sewer hose that will last. Polychute ( has developed a type of sewer hose that will probably last longer than the motorhome.

In addition, Polychute is a leading proponent of developing a written standard for waste hoses. It’s a sanitation and health issue, and I wouldn’t be surprised to see minimum standards for hose thickness and materials adopted by NFPA in the future. Personally, I would like to see the sewer hose become a permanently installed component on the motorhome, as some forward-thinking manufacturers do now, thereby eliminating the need to connect, rinse, disconnect, and stow a nasty hose at every evacuation.

Termination Connections

For decades, the method used to attach the sewer hose to the motorhome termination assembly has been to first attach the hose to an adapter fitting with a common hose clamp and then connect the adapter fitting to the termination assembly by twisting and locking it onto a bayonet fitting. We’ve all seen those four little nubs on the termination connection; that’s the bayonet fitting.

Although these fittings have been in use throughout the modern era of RV holding tanks, an inherent drawback to this methodology exists. Think about it; twisting a round pressure fitting with an integral 360-degree rubber-like seal against a hard plastic surface ultimately will distort the seal. In some cases, where the plastic bayonet fitting has become nicked or otherwise damaged, the seal in the adapter fitting literally can be destroyed by the twisting motion needed to attach it. Take a walk through any campground and see how many sewer fittings are actually dripping waste onto the ground right at the site. Likewise, it’s not uncommon to see termination assemblies with the cap in place, still dripping moisture from the holding tanks as the coach travels down the road. The sewer cap is twisted into position onto the bayonet fitting just like the hose adapter. Interestingly, bayonet fittings are not used in any other industry for the transfer of liquids or waste. Literally every other industry uses a type of compression fitting, a threaded connection, or a fitting with a cam-type locking mechanism.

A cam-type locking waste connection that eliminates the twisting required by the bayonet attachment is now available for RVs. Check out the Waste Master Cam-Loc produced by Drain Master. Any bayonet fitting can be converted to the newer Cam-Loc connection. A cam-type mechanism nullifies the twisting action and results in a secure, leak-free connection. During my testing, I could not “make” it leak, even on purpose. And this also eliminates the possibility of rusted hose clamps that, once contaminated by virtue of their proximity to human waste, become a health risk if an errant RVer slices a finger while trying to secure the hose onto the bayonet fitting. Oh, it does happen!

The Other End

Just as important as having a leak-free connection at the termination assembly on the motorhome, avoiding leaks and spillage at the connection into the sewer inlet is, for the safety and comfort of everyone, also crucial. Since no universal sewer inlet size is mandated for RV parks or dump stations, you’ll find inlet sizes that range from 3 inches to 5 inches. Always use a progressive, stair-stepped, or tapered doughnut gasket to ensure a tightly sealed connection into the sewer inlet. Avoid simply sticking the open end of the sewer hose down into the inlet and placing a big rock against it! Believe it or not, this practice is more common than one might think.

In addition, I firmly recommend a sewer hose equipped with a positive shutoff nozzle at the sewer inlet end. Both the Waste Master hose from Drain Master and the Polychute hose have the same, multi-seal, positive shutoff mechanism on the nozzle. This not only permits a surefire method of stopping the flow, but when the supplied cap on the motorhome end is affixed, all odors are locked inside the hose itself during stowage. Tell me you haven’t opened a plumbing bay (yours or someone else’s) and instantly realized a sewer hose was stowed somewhere in the compartment.

Correct Waste System Evacuation Procedures

1. Always wear disposable protective gloves when handling any waste system component, and be sure to wash your hands thoroughly afterward.

2. Connect the sewer hose. Begin by inserting the nozzle end of the hose into the campground sewer inlet or dump site, and open the valve on the nozzle. Walk back to the termination assembly on the motorhome, extending the hose only the distance required. Always avoid snaking the full length of the hose back and forth on the ground. If more hose is needed to reach the motorhome, simply attach an extension hose when necessary. All quality hose makers offer extension hoses and connectors. To complete the connection, remove the protective cap or plug on the motorhome end of the hose and attach it to the termination outlet. Be sure to maintain the proper slope of the drain hose from the termination outlet to the sewer inlet.

Employing the “first in, last out” rule — inserting the sewer end first and removing it last — will guarantee that no waste water is released and avoid further contamination on the ground. Note: this is only applicable if the hose has a positive shutoff valve on the sewer end and a cap or plug on the coach end.

3. Evacuate a holding tank (black or gray) only when it is more than three-quarters full. Yes, contrary to what some veteran RVers may tell you, this means leaving the gray valve fully closed while in the campground. Filling each tank to a level above the three-quarter mark before evacuating will ensure you’ll have enough volume (and velocity) to thoroughly drain the tank and flush the hose.

Here’s another reason for keeping the gray holding tank valve completely closed except during evacuation. Have you ever walked through a beautiful, scenic campground and caught a whiff of sewer odor? Kind of ruins the moment, right? All motorhomes with the gray tank valve in the open position (sewer hoses obviously connected) are simply acting as a direct conduit to the park’s sewer system. Each motorhome becomes a mini-vent of sorts, in parallel with the septic system of that campground. No wonder sewer odors abound at even the nicest destination sites.

A large septic system in a campground will have fundamental venting designed into it. However, with numerous RVs with their gray tank valves open connected to the system, odors can rise up through the park’s septic system, through the sewer hoses of those coaches, through their empty gray holding tanks, and up the vents of those holding tanks. Remember, it may be your gray tank, but it’s the campground’s black and gray odors coming up and through it. The biggest problem with this scenario is that the gray tank vents on RVs are a lot closer to the ground and more prominently located than the park sewer stack, so odors are more noticeable. By keeping the gray tank valve closed until the tank is almost full, you will eliminate the localized venting of the campground sewer gases at your particular site. The more RVers who follow this precept, the less likely we’ll have to endure septic odors in and around the campsite.

4. Evacuate the black tank first. This is pretty much standard procedure and something most motorhome owners are aware of, but it’s worth mentioning again.

After the black tank empties, flush it out with a large amount of fresh water when connected to city water. Simply keep flushing the toilet while the termination valve remains open. If you opt for the Polychute or Drain Master hose, monitor the cleanliness of the water through the integral Clear-Vu fitting as it drains. There are other clear fittings available for bayonet-type hose adapters as well. If dark or grimy water persists as the tank is flushed, close the valve and completely fill the tank with fresh water and evacuate again (and again, if necessary). When the draining water is relatively clear, stop flushing; close the gate valve; and add enough water to completely cover the bottom of the black tank.

Permanently installed holding tank spray kits that attach to each holding tank and allow fresh water to be directly sprayed into the tank after dumping are available in the aftermarket, but I’m hesitant to drill mounting holes into holding tanks. Plus, I like to flush all components of the waste system, including the toilet, sink drains, etc., so I prefer to simply flush the toilet and run water through the sinks.

5. Evacuate the gray tank last. After the black tank has completely emptied and its termination valve has been properly closed, open the gray tank valve and empty that holding tank. Be sure to rinse this tank as well. Dumping the gray tank last utilizes its liquid contents, as well as the fresh water introduced after dumping, to help wash away any solid waste that may remain in the sewer hose.

6. Drain the sewer hose. After both tanks have been emptied for the last time at that location, take the time to thoroughly rinse the sewer hose with fresh water until clear water is viewed through the Clear-Vu fitting on the sewer hose. After closing the gray termination valve, remove the sewer hose from the termination outlet on the motorhome and, if so equipped, secure the plug to the hose and the termination outlet. Then begin “milking the hose.” In other words, raise the hose at the motorhome end and walk it toward the sewer inlet. Keep raising the hose as you walk, thereby emptying it completely of water. Even a properly sloped flexible sewer hose may have residual water and waste particles left inside. An accumulation of these particles will cause odors over time, so it is imperative to completely remove as much moisture as possible.

7. After milking the hose and as you reach the campground sewer inlet connection, close the positive shutoff valve on the sewer nozzle and disconnect it from the campground sewer inlet. Remember the “first in, last out” rule! With the cap on the motorhome end of the hose and the nozzle valve turned off on the sewer end, all remaining odors stay inside the hose. Cap the sewer inlet, stow the hose, and add an enzyme-based additive to all holding tanks.

8. Check the P-traps. Unless you have upgraded to HepvO waterless sanitary valves, look down each sink drain and the tub/shower drain every month or so to ensure the water seal is still there. In some waste system configurations, a quickly draining tank can cause the water lock to be siphoned out of the trap. You’ll probably have to use a flashlight to see down the drains, but it is essential that a water lock remain at all times. Remember, this is the primary method of preventing gray holding tank odors from entering the interior of the coach. Bottom line: a dry P-trap is nothing more than a shortcut for odors to gain entry into the motorhome.

9. Be sure the toilet bowl contains water at all times. If water eventually seeps past the seal and the toilet bowl empties, it’s time to make an appointment at your local service center. An empty toilet bowl will permit black tank odors into the coach. If water can leak past the seal, odors can as well.

Being proactive when it comes to the waste systems on the motorhome will reap its rewards. If anything, it will ease olfactory torture to a certain extent. And that will benefit us all. Remember, RVing is more than a hobby; it’s a lifestyle!

Safety Tips

Always take extra precautions when working on the motorhome waste plumbing systems, even when simply evacuating the holding tanks. Always wear disposable gloves when handling sewer hoses and connections. Many coach owners have installed a glove-and-disinfectant dispenser right in the waste plumbing bay as a reminder.
When using hand tools while working on the waste systems, be sure to clean and disinfect them after each use. Those same tools may be working on the fresh water system next! A can of spray disinfectant is also a handy item to carry with you as you travel.


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