Foul Odor from Toilet


New Member
Recently I purchased a 1993 Breakenridge 37' trailer (1st timer) and have a few questions. First and most annoying is the foul odor from the toilet. I'll use the trailer on the weekends and have the holding tanks pumped on Tuesdays but by the time I get there the following Saturday the place smells very bad. I do place a deoderizor and about a gallon of water when I arrive and as the day goes on the ordor subsides but I can't live with this. Are there any suggestions of how to correct this situation so it does not smell at all?

DL Rupper

Senior Member
Foul Odor from Toilet

Hey SKB, welcome to the forum. Checkout The Geo Method/Black and Grey Water Holding Tanks, RV Tips & Tricks RVUSA Forum. The info should help. Also check on your roof to make sure your holding tank vents are not clogged/plugged.


Senior Member
Foul Odor from Toilet

If you only use it on weekends, and dump the following Tuesday, you may not have enough liquid in the tank to provide a complete dump (leaving solids behind, which will cause stink). Or the previous owner may not have maintained the tank well.

Is the odor only when you are flushing, or all the time?

If the former, its likely either not being well cleaned, or the vent tube is clogged as DL suggested. If is it the latter, well some toilets have an overflow tube which can be broken, poorly installed or the P trap dried out, and this is a direct path for any smell to get into your RV. In either case, running a vent fan over the toilet while dumping (or not in the case of the overflow tube) can encourage odors to enter the RV.

Use lots of water when you use the toilet. Check out the Geo method DL refers to or try an enzyme-based chemical and/or deoderant. Flush the tank after you dump (internal flush, back flush or toilet wand). Don't leave your valves open if you are connected to the sewer long term (allows sewer gases to get back into your RV). If the vent is not clogged, add a RV360 cap or a 'lil stanker' fan to it.

If your tank is not full when you want to dump it, fill it with water before dumping.


Senior Member
Foul Odor from Toilet

What is put into your tanks does smell bad, and no home remedy or commercial product will do much to help if your tank vents are not clear, and it sounds like that may well be the problem. Each holding tank has a pvc pipe that runs from the RV roof down into the tank to vent the air from the tank. On the roof there is a cap over that vent to prevent the entry of rain into the tank. There are several things that can be a problem with the vents. I would remove the cover from each vent and first use a garden hose to run water into it to make sure that the vent pipe is open all of the way to the tank. Bugs sometimes use the vents to make nests in and plug them up. If they are not clear, gently run some stiff hose or plastic of some type through them to clear any obstructions. Once you know that they are clear, check to be sure that the vent pipe has no gaps that would allow the odors from the vent to enter into the RV around the top of the pipe. If they do, plug that area with caulk to seal it. When you put the vent caps back on, you can also replace them with vent covers that are a venturi that will keep a slight vacume in the tank any time you travel or if there is any wind. One version even revolbes with the wind to change the direction it points to work best. I don't have those but have heard really good reports on them.

According to a seminar that was put on by Thetford, manufacturer of RV toilets and sewer system equipment, the best way to clean the tanks is to fill about half full of water and then use the detergent, trisodium phosphate (TSP) that can be found in the wallpaper department of any home store. Mix the TSP in a gallon or two of water using the amount that the directions call for for the amount of water that you put into the tanks. Once you do this, drive the RV around for a while, where you make turns, stop & start and such to agitate the mixture. It would not hurt to let it sit for a day with the detergent in the tanks and then do it a second time just before you dump. That should remove any built up residue unless it is very excessive and thus allow you to start with a fairly clean tank.

Also, as mentioned above, most toilets do have an over-flow that has a P trap in them. If that P trap is empty it will vent into the RV. To be sure that it is full of water, just fill the toilet with water until some water goes down that over-flow.

If you tank vents work properly and if the tanks are fairly free of debris, you should not need to add anything to them except in very hot weather. As long as you do not introduce some chemical into the tank that will kill the natural bacteria, it will break down naturally and become a liquid as long as you use plenty of water. You will find that most of us who are fulltime use lots of water in our tanks and very seldom anything else. But since your RV is used, the previous owner may have left a lot sticking to the inside of the tank so I would do both of these things first.

You will find that there are many different opinions on what works best, but these are the things that an RV shop would do first.