No one likes the odors from your holding tanks. No one. But if you smell a rotten or sewer gas-like smell when you turn on your furnace, something is amiss. Time to do some diagnostics.

Ah, RVing. It’s always something, isn’t it? Well, here’s a new one: You smell sewer gases or something like it when you turn on your RV’s furnace. Now what? Let’s take a look.

What could be the cause?

One possibility is that sewer gases from your toilet, sinks, or shower are being drawn in through the furnace’s return air duct. This is a bit more likely when the tank release valves are open; another reason to keep them closed unless you are emptying and flushing your tanks.

Another reason for those sewer gasses to be drawn in could be that there is a problem with your vent pipe(s). Some sink drains use a one-way vent that is supposed to open while water is flowing and close when it is not flowing. Other sink/shower drains have a sewer vent pipe that runs up to the roof. In either case, you could have a problem with the sewer vent pipe – the one-way vent could be stuck, there could be a break or blockage in the vent pipe, etc.

You might also want to check your toilet. A slipped or broken wax ring, shift in the toilet off of its seating, or crack in the toilet could be the cause of your problems.

A second possible cause is a problem in your furnace ductwork itself. It is possible something has gotten into the furnace ductwork and is sitting there rotting or moldering away.

What do you do next?

Here are some things to check if it’s not your furnace itself:

Before you do anything make sure that your dump valves on both your black and grey water tanks are closed. If they are open they will definitely allow sewer gasses into your RV.

Run water into all of your drains to make sure any of your “P” traps (if your RV has them) are full of water. If you don’t have “P” traps and have check valves instead, make sure those are not obstructed or broken (some models have delicate soft rubber or thin plastic valve mechanisms).

Carefully go up on top of your RV’s roof, take the caps off your vent pipes, and peer down the pipes. Look for any type of blockage. Also while you are up there, to try gently press down on the pipe. If it moves it may be the source of the problem. The connection may be broken where it goes into the tank. Be very careful – you do not want to create a new problem like a leak in the roof or a broken pipe or fitting.

Go to your plumbing bay or on the outside of your rig and inspect the holding tanks. Look for any obvious signs of leakage especially around the top of the tanks. If they are enclosed then the problem will be more difficult. Just look for leaks.

Figure out where the furnace is drawing its air. It should be from outside of the RV. In this step, turn the furnace on and go outside to the fresh air intake. Is it blocked?

Use a flashlight to look into the air intake/grate, make sure nothing is in there. If the air intake is clear, do you smell the sewage smell near the access door to the furnace? Open the access door and smell around it. Can you smell the sewage? If no smell is detected, then the problem is in your ductwork.

In conclusion

Sewage smells don’t just happen in your holding tanks, but that’s where they may originate and spread from. Keeping your tanks clean by following smart and correct tank processes; not using enzymes, biological agents, or harsh chemicals in your tanks; and being rigorous and thorough in your holding tank cleaning and flushing procedures can help to keep problems from happening.


Jim Tome, Owner

Jim Tome, Owner

Hi, I'm Jim Tome and, along with my wife, Debbie, the owners of Kleen Tank LLC, the national leader in RV holding tank cleaning service. We've been RVers like you since 2004 and have traveled all over the U.S. in our Airstream travel trailer. We started the business about twelve years ago and have cleaned tens of thousands holding tanks in thousands of RVs. From tiny weekend travel trailers to monstrous fifth wheels to luxurious motorhomes, I've seen just about every situation there is with RV holding tanks and waste systems. I hope you enjoy our articles; I try to post at least one per week and we've got a great library of them to cover just about every problem. Enjoy!


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