Settle a debate regarding sewer hose/smell

Might not be the black tank. Could be a faulty air admittance valve under one of your sinks.

Also, if you have an exhaust fan running in the commode room when you flush that could bring extra odors up from the tank.

You're keeping waste valves closed until you need to dump?

The hose can stay on as you will keep the "grey" water tanks open. The black tank should only be drained when its full. You will want to check and make sure the toilet bowl holds water, if dry will allow the sewer smell to come up. You might also want to check the vent pipe on the roof. Make sure its clean you can run a hose down and flush it out if needed.

Dump your black tank completely. Then pour in a bottle of bleach, and fill the rest of the tank with clean water. Let it sit a few minutes. Shake the trailer so it will mix real good. Then dump the tank. Do a second short rinse to get the bleach away from the valve slide so it won't hurt it by sitting too long. Smells should be gone, unless you have another problem occurring somewhere else.

when air is on, could be pulling from black tank

First do not leave the holding tank valve open. Keep it closed until the tank is 3/4 full and then open the valve to dump the tank.

Next step is to check to make sure the vent for the holding tanks on the roof are clear and not blocked by debris or nest.

Next check the toilet gasket to make sure it is seated properly and not hardened. If this is a used RV the gasket may need to be replaced. They go bad every 5 to 10 years depending on conditions.

Third you may need to sanitize your holding tank. This will require the use of lots of water some travel and a couple of bags of ice. Fill the tank full of water with the appropriate amount of Thetford Aqua Khem deoderizer. Let it sit overnight. Drain the tank. This will help moisten any leftover "stuff". Fill the tank about half full of water, add ice out of the bags and go for a drive towing the 5th wheel over a bumpy and or winding road. Drive for at least a half hour or hour. Dump the tank. Fill full with water and dump.

If you don't want to tow the 5th wheel you can try filling and dumping the holding tank several times. Keep the holding tank valve closed while filling the tank.

there is a great debate about putting bleach into a black or grey tank. many professionals say it kills the needed bacteria in the tank. I think the smell you smell might be from the grey tanks. they can stink like the blazes also. there is a product out there and you can do a web search for it, it is called "Happy Camper". this is by far the best I've ever used to control smell in black or grey tanks. I use it in both. I have used just about every thing on the market for smell and this stuff is worth the money.

I keep both the gray and black valves closed until I dump. And once empty, both valves get closed again. I don't want "anything" coming into my rig from the park. A properly vented system should keep the sewer smells out of the rig.

Consider The Geo Method to clean your tank.

old guy wrote:
there is a great debate about putting bleach into a black or grey tank. many professionals say it kills the needed bacteria in the tank.......

I don't know why you would care about having bacteria in the black or grey tanks.....they are only holding tanks, not a septic system

The smell is probably coming from the vent through the roof. Sewer gas is heavier than air and the vent is never very far away from your bathroom exhaust fan. The fan covers are not air-tight and the sewer gas will make its way under them and into your camper. You will notice it mostly on calm days. I'm a plumber and I deal with this stuff all of the time in houses.

Bruce