Being familiar with the variofus components of a motorhome’s waste plumbing systems, and performing regular maintenance, can help owners avoid the “big stink.”
By Gary Bunzer
Gather two or three motorhome owners, engage them in a discussion of RV plumbing systems, and the discourse invariably will turn to one of the most displeasing, yet necessary, aspects of RVing: waste containment, evacuation, and sanitation. Dumping the holding tanks, a relatively simple process, can, in some cases, cause more consternation (and operational problems) than one would expect. As disagreeable a chore as it may be, given the technology available today, plus heightened environmental awareness, there is a renewed vigor to properly store, evacuate, and maintain the waste plumbing system on all RVs.
There have been some interesting product and process advancements in many areas of waste plumbing, so with disposable gloves in hand, let’s spend some time investigating improved waste management practices and learn about a few products that may allow us to lessen our burden.
While many people will start and end their discussion about waste management with the black and gray holding tanks, the system is much more complex. From my perspective, once fresh water leaves any faucet and showerhead or enters the toilet, it becomes waste water. So begins our management of it.
One of the most common complaints from RV owners is the proliferation of obnoxious odors emanating from the waste plumbing system. Nothing can ruin an excursion faster than having holding tank odors permeate the interior of the motorhome. The first line of defense against invading fumes is the water lock established by P-traps located below the sinks and tub/shower drains.
Long a staple in the plumbing trade, the common P-trap has served us well for many years. However, there is a downside to this type of hardware, especially concerning motorhome P-traps, which generally are used less often than those found in commercial or residential applications. Oftentimes the water seal in a motorhome P-trap is diminished or lost altogether. The jostling that occurs while traveling, improper siphoning action during highway turns and tank evacuations, or simply drying out from nonuse can render the water seal ineffective at preventing holding tank odors from entering the living area of a motorhome. In addition, the P-trap requires diligent maintenance; frequent cleanings and freeze protection are necessary and often overlooked. If neglected, waste residue inside the traps can foster bacteria growth and subsequent odors from within.
Enter a new product, the HepvO waterless sanitary valve. Available in the aftermarket and now being used as original equipment by some manufacturers of new motorhomes, the HepvO waterless valve replaces the common P-trap, thereby creating an effective seal against odors while providing additional storage space. (Who reading this would not appreciate having more room for personal effects?)
This ingenious valve is con-structed with a self-sealing, flexible, silicone-derived membrane that allows water to flow through it but completely closes off when water flow stops, thereby preventing holding tank odors from migrating up and through the sinks, tub, and shower. The HepvO also is an effective air-admittance device, which eliminates the need for mandated antisiphon trap vent devices (ASTVDs) at a fixture’s P-trap arm.
With no standing water, as is necessary in a P-trap, the HepvO waterless valve eliminates the possibility of bacteria growth and eliminates freeze concern and evaporation issues. (To see a short RV Doctor video about the HepvO, visit www.youtube.com/watch?v=6tS7t35vw6E.)
As for the toilet, I probably do not have to remind everyone to keep water in the bowl at all times, although that may become a challenge when the motorhome is stored for a lengthy period. Still, with water in the bowl, you are guaran-teed that no holding tank odors can escape into the living areas of the motorhome.
If you find the toilet will not hold water, chances are it is time to replace all the internal seals and gaskets. You’d be surprised how many seals are used in an RV toilet! Dried out toilet seals are the primary causes of black tank odors permeating the interior of the motorhome. Most toilet manufacturers package gasket repair kits for their line of toilets. And unless you swap out toilets regularly, chances are this type of maintenance will be necessary at some point during your RVing career.
To test whether the toilet water seal is leaking, simply place a light pencil mark in the bowl at the level of the water after a normal flushing process and observe it over time. As I state in my seminars, if water can seep past the seal, odors eventually will come up from the holding tank.
Waste System Venting
Motorhome manufacturers typically rely on National Fire Protection Association (NFPA) 1192, Standard on Recreational Vehicles, as the guiding standard for how waste plumbing components are designed, listed, and installed. The NFPA 1192, which has been adopted and endorsed by Recreation Vehicle Industry Association (RVIA), is edited every three years in order to keep up with new designs and technological improvements to better serve the entire RV industry.
Parts of this document specifically address the subject of holding tank venting, which is required for both the black and the gray water systems. The method chosen by most RV manufacturers is to run a length of ABS pipe from each holding tank up and through the roof of the motorhome. The importance of proper venting cannot be overstated, especially as it relates to odor control. In addition, without correct venting, sinks will not drain properly, bacteria can propagate, and holding tanks will not drain as quickly or completely.
Keep in mind, as a holding tank empties or a sink drains, fresh air must enter the drainage system. Since motorhome fixtures and holding tanks rely solely on gravity to empty, having air enter the sys-tem as sinks and tanks are drained results in a faster and more thorough process. Two types of vents are used in motorhome waste systems: direct exterior vents and the aforementioned anti-siphon trap vent devices (ASTVDs).
Direct vents connect the waste systems (either within the drain piping or directly from the holding tank) to the atmosphere outside. As mentioned earlier, most motorhome manufacturers install a vertical section of plastic ABS pipe up and through the roof of the coach for both the black and gray systems.
There is one other type of direct vent: a side-mounted vent. Side venting is permissible only in the liquid waste system, usually from a single fixture, and typically is used only on the smallest recreation vehicles. Clearly, the most common and the most effective waste system vents are those that protrude above the roof.
An anti-siphon trap vent device (ASTVD) is a handy gadget used as a secondary vent to aid in draining sink fixtures. Also called “check vents,” ASTVDs allow air into the drainage system but prohibit air from passing out of the system. ASTVDs are installed in the liquid drain piping system at or near a P-trap inside a cabinet. Look under the kitchen and lavatory sink area and you should find them. They are mounted at least 6 inches above the P-trap’s horizontal arm. ASTVDs have an integral atmospheric pressure-controlled, rubberized, one-way valve that prevents odors from escaping into the living portion of the RV. In other words, air is allowed in, but not out.
In addition to ASTVDs, there must still be at least one vent protruding through the roof to allow gases out of each holding tank. ASTVDs do not act as primary vents. The better-designed waste systems will have ASTVDs installed at every P-trap as well as a direct vent running from each holding tank up and through the roof. Remember, though, with the advent of the HepvO waterless sanitary valve, ASTVDs are not required. Since the HepvO eliminates the necessity for an ASTVD and a P-trap, there should be more cubic inches of storage space under every sink. With HepvO valves, manufacturers can eliminate the cost of P-traps and ASTVDs (and their associated fittings, Ts, and piping), as well as those prone-to-leak shower-mounted skylights, while gaining extra storage space. The reason so many motorhomes are equipped with skylights inside the shower enclosure is because of the height needed to raise the shower pan to allow for a P-trap. Without a P-trap, the shower pan can be lowered and the skylight eliminated on many floor plans.
If I were a betting man, I’d wager not many RVers have ever given serious thought about performing maintenance on the waste system’s direct vents. But here’s something to investigate if you’ve never done so before. Sometimes motorhome manufacturers cut a very large hole in the ceiling and roof for vertical vent pipes to pass through. The large hole obviously makes installation easier and faster. Oftentimes, this opening is not sealed properly all the way around the outside perimeter of the pipe. In other instances, the vent pipe itself may not extend far enough above the roofline. According to the NFPA 1192, “each vent pipe shall pass through the roof and terminate vertically, undiminished in size, not less than 2 inches above the roof.”
In any scenario in which a short vent pipe is used (extending less than 2 inches above the roof) and the vent opening routed through an oversized hole and not properly sealed, tank odors can pass up the vent, collide with the underside of the sewer vent cap, and be forced back down around the side of the vent pipe and into the ceiling area, where they eventually migrate to the living area.
It would behoove the serious motorhome owner to remove the top cap of each sewer vent on the roof and ensure that the space around the vent pipe is sealed tightly and that the pipe itself stands at least two inches above the roof. If necessary, extend the vent by using a common ABS coupling and a short piece of pipe.
In addition, depending on how the vent is attached to the top of the holding tank, vent pipes have been known to fall down inside the tank below the surface of the waste, nullifying any venting action whatsoever and allowing tank odors to exit the open end of the vent virtually within the ceiling void or even inside an interior wall pocket. By inspecting the vent termination on the roof regularly, this can be avoided.
As for ASTVD maintenance, the rubber membrane employed in ASTVDs can sometimes dry out and become stuck in the open position. If holding tank odors are prominent under a galley or a lavatory cabinet near the P-trap, chances are it’s time to lubricate the rubber seal inside the ASTVD. Use Dow 111 lubricant to moisten the rubber diaphragm. Since it is located above the actual flow of waste water, the ASTVD is simply threaded into a fitting above the trap arm and usually can be removed for inspection and periodic lubrication.
Anti-Odor Vent Accessories
Although NFPA 1192 mandates certain products and practices for the motorhome manufacturer, it does not require the inclusion of caps on the direct vents protruding through the roof. Manufacturers that do install caps at the factory do so to keep objects and critters from entering the open end of the vent stack. But typical roof vent caps or covers are not intended or designed to control or aid in odor elimination.
It is quite common to see a couple of open-ended, 11/2-inch ABS vent pipes, uncapped, on the roof of the motorhome. They will be sealed, however, by a flashing of some type to keep moisture out of the roof and ceiling areas. But open-ended vent pipes, and even those covered by typical caps, can actually create odor problems for the RVer. The dynamics of airflow (side drafts, downdrafts, and updrafts) all create a higher atmospheric pressure inside the holding tanks. This forces odors to escape into the interior of the motorhome through dried out P-traps, empty toilet bowls, faulty ASTVDs, internal toilet hoses, or any other air leak in the venting or drainage system.
But as you’ll often hear me state, thank goodness for the aftermarket. Today, several companies produce excellent add-on devices for waste vents that actually can help eliminate holding tank odors altogether. Coil n’ Wrap (www.coilnwrap.com; 866-603-8388) makes an all-metal rotating device I have installed and tested called the Xtreme Vent. Another company, 360 Products Inc. (www.360productsinc.com; 604-715-6072), produces a nonmechanical vent cap marketed as the 360 Siphon, which is designed to grab the slightest breeze and literally suck the fumes out of the holding tanks. Both products utilize a combination of Bernoulli’s Principle and the Venturi effect. (I won’t bore you with the details here.) Suffice it to say that the Xtreme Vent and the 360 Siphon will produce negative pressure inside the holding tank and vent stack, thereby drawing odors out of the tank. I have faith that either of these products will be beneficial to all motorhome owners suffering from holding tank odors.
Gravity is a vital decree that coach makers must adhere to, along with anyone who repairs or modifies the waste plumbing system on the motorhome. The force behind any sink drain and holding tank evacuation is gravity, and we all know liquids will not flow uphill. Without the proper slope, drainage can be slowed, plugged, or otherwise negatively affected. If you have experienced improper drainage at any receptacle or holding tank, perhaps a close inspection of the slope of each drainpipe and holding tank termination assembly is in order.
According to NFPA 1192, horizontal runs of waste piping should slant toward the holding tank no less than 1/8-inch per linear foot. Also, the waste piping should be supported not less than every four feet. If the pipes are allowed to sag or slope upward, waste water can be trapped inside the drain system and become a breeding ground for bacteria as well as odors.
ABS plastic fittings used throughout the drainage system must be designed with an integral slope of 1/4-inch per foot. I have witnessed unknowing RV service technicians install elbows, tees, and wyes not meant for RV waste systems even though the exterior design of the fitting looked correct. Typically, the built-in slope is molded into the internal portion of the fitting. This shouldn’t be an issue as the coach leaves the factory, but can become a problem if plumbing repairs are performed improperly by noncertified technicians in the field.
In Part 2 of this article, I will go Into a detailed examination of the holding tanks, covering addivites, monitors, and blockages, as well as termination valves and their maint4enance, connections, the sewer hose, and more.
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.