Horrible Odor

I did not hear anything about you using black water chemicals in the tank.  Assuming you are not, always use it.

At the campground, keep the black water tank valve closed until time to empty it. 

Sounds like you are already flushing the tank regularly.  I use the "Hydro-Flush" which is available from Camping World, Walmart, etc.  It really blasts water into the black water tank.

Nothing is wrong with your tank.  The pod tanks are all built with a sag to promote better drainage and ease of flushing.

The only source of odor that I can think of is lack of chemicals, or an inadequate amount of them.

Bob

I agree with Bob and PeggyL. If you're not using chemicals in your black water tank, start using them. If you're already using them, then your system may have a venting problem of some sort. Add water to the shower drain like Peggy says. Also make sure the slide valve closes all the way when you flush. Make sure both outside dump valves are fully closed.

-- Steve

Do you leave your gray water valve open while camped? I used to do that and sewer gasses would work their way back up and fill the trailer with stink. Now we just just empty the tank once or twice a day. The odor has never reoccurred. I know our shower trap had water in it, but somehow the gasses made their way up through it or the kitchen sink. I don't quite understand how this happens. Gray water doesn't usually smell that bad and the gasses would have to go up the hose, bubble up through the gray water in the tank and then make it through any traps filled with water. It all seems unlikely, but I can assure you it made a huge difference. Under any circumstances, never leave the black water valve open except when dumping a hopefully close to full tank.  You do not want to regularly dump; the black water tank. It is better to let it get as full as possible before dumping. You want as much pressure as possible when pulling that valve open. Otherwise something may get stuck in the gate and I can assure you, that is a 0 on the fun-meter.