Troubleshooting RV Sewer Odors

Troubleshooting RV Sewer Odors

Question: We have a "sewer smell" in our RV.

Answer: Several things can cause that problem. Let me run down the list, you will have to check each to see if they may be the source of your problem.

For one reason or another many manufacturers use one-way plumbing vents on the bathroom and kitchen sink drains. These are one-way valves, when working properly. The problem is they do not always work properly. When working properly, they should prevent tank odors from entering your RV. These one-way valves employ a spring and diaphragm that should only allow air INTO the plumbing system to vent it, like a normal roof vent would, when water is moving through the drain pipes to the tank. The diaphragm is supposed to shut and prevent any fumes or that "sewer smell" you are referring to from entering your RV. Check under your sinks and see if you have these one-way valves. Let's make sure you are looking in the right place, you are looking on the drain line aren't you? If you have these one-way valves they will be on the drain line between the "P" trap and where the drain pipe enters the wall. The one-way valve will not have a handle on it like normal valves, this one is automatic as in spring loaded. If you locate one of these one-way valves, the next step is to unscrew them for an inspection. You may either have a faulty valve or some debris is keeping the valve's diaphragm from seating. The problem may be obvious such as a dry rotted diaphragm. If the problem is not visible, a good cleaning may fix the problem or you can purchase a new vent valve at most plumbing stores and home centers. In your friendly Lowe's or Home Depot they may refer to these valves as a "cheater vent". They are used in normal stick and brick homes as well as RV's so a replacement should be easy to find.

If that doesn't remedy the problem check your toilet. There are many different makers of toilets and many different models within those makers so you will have to use a little thought on this one. There is an "overflow" hole at the top of most of the plastic Thedford toilets. You will most likely never spot this overflow hole unless you get down close and look for it. It will be about 7/8" in diameter. Look for this hole somewhere near where the water enters the toilet. This overflow hole is attached to a hidden 1/2" hose that leads to the black tank in case there is a problem and the toilet starts to overflow. This 1/2" hose will have a loop in it that performs the function of a P-trap in your home plumbing system. If water evaporates from the loop then there is a direct path for "sewer-gas" to make its way from your black tank into your RV. All you have to do here is to pour some water into that "overflow" hole and that will reestablish the vapor lock function. It will not take much water, a 1/2 cup should do the trick.

If the smell is still with you then check the seal between the toilet and the pipe leading to the black tank. I have heard that people have found these to be improperly installed thus allowing sewer gas to enter the RV.

If these don't fix the problem you are on you own. I don't have any more advice.

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