Sewer smell when using exhaust fans

Personally I leave the gray tank closed until it's dumping time.

The smell is from a faulty air admittance valve as mentioned above. It will unscrew you just have to sometimes work at it for a bit. Get a replacement from Home Depot and the smell will be gone.

Ya'll make my head swim.. do this, do that, no, not that.. THIS.
A P-Trap is in your house for just that same reason and it works.
Now, for a Newb TT camper Why wouldn't you want both black and grey water valves to be be closed? That seems like the best way to keep from siphoning fumes and from sucking up stench. It's a simple air flow issue, exhaust fan creates a negative air pressure in the cabin. Air comes from the open grey tank into the cabin to make up for it. That is why the suggestions for cracking the window help.

Here is a simple experiment to help at home in the "off season".
1: Put a quarter in the palm of your hand.
2: Now put your vacuum cleaner hose over the quarter sealing tight against your palm
3: Next turn on the vacuum cleaner. Hold the hose tight against your palm...
4: Turn off the vacuum cleaner
5: Once the vacuum dies down, remove the hose from your palm

Where's the quarter?

In your palm! Since there no air flow to draw the quarter it stays put! If your had lost the seal against your palm the quarter would have been sucked into the vacuum cleaner.
If you close the grey and black water valves there is no flow and the negative air pressure caused by the exhaust fan would be supplied from elsewhere. Your TT is NOT air tight, so it will get the replacement air from somewhere, but opening a window wouldn't hurt.

I have an Open Range RV also and had the *exact* same problem. Like others have said, it's the air valve under the sink. Until you can replace it, a temporary solution is to rubber band a zip lock bag over it. I did that because ours failed in the middle of a trip and the smell went away. The grey tank still drained fine also, maybe just a touch slower.

wrenchbender wrote:
After rinsing the grey water tank pour about 2 cups of ammonia down the sink drain and let it set for an hour.

Be very careful not to add bleach to the ammonia or you will make mustard gas and you might not wake up in the morning after that. I personally stay away from ammonia.

When we use the vent fan, we crack open a window.
My theory is so it doesn't create a vacume effect.

VintageRacer wrote:
Make sure the black and the grey tank both have good vents to the roof of the trailer. The can share the same vent line (1.5"{ ABS is good) and it can be connected to the drain line from the sinks to the tanks. The vent line will allow the sewer gases to escape vertically from the tank, and will relieve any pressure inside the tanks that might force gases past the P-traps. Don't forget that you always have to refill the P-traps after dumping, the suction sucks them dry.

Brian

If vent lines are good, dumping should not suck p-traps dry.

We do use grey tank treatment from time to time and usually based on what food we're fixing....fish or something that would get a funky odor quickly from the wash water. We always leave the grey tank closed. If we are find that the tank needs to be dumped sooner rather than later, DH will dump it and then close up again. We've never had an odor problem and, while I had never considered it, the odor coming from the sewer itself makes sense to me. Suggest you try that first. Don't know that I'd put ammonia into the plumbing in case it's not compatible with some of the lines, etc. But a healthy dose of baking soda certainly would not hurt anything. Dump some in - maybe a box per drain - add some water and let sit, then rinse well. Couldn't hurt. Good luck.

After rinsing the grey water tank pour about 2 cups of ammonia down the sink drain and let it set for an hour.

It should not be glued on. They are threaded. I thought mine was glued, but realized it was screwed into a union fitting. I was trying to unscrew the union instead of the valve (the union is glued to the pipe). The valve in a male and the union is female. When you try to unscrew it, try turning from the top. It should be pretty easy to remove.

Cool Canuck wrote:
Here's a secret. Put something under your sewer line to create a P trap or do something similar to trap water in your hose. This will prevent sewer gasses from coming back up your hose and through your tanks and vents.

That's a darn sure cure if it isn't freezing. Simple but would be totally effective.