Triple Slide Jayco said:
I rinsed my black tank the other day after dumping and it held quite a bit of brown that I thought would have came out by itself, I was surprised. The OP may have the pyramids of egypt growing if they dont rinse the black tank.
I've installed a tornado flush kit in each of my last two travel trailer black tanks.
https://www.amazon.com/Camco-40126-Tornado-Rotary-Rinser/dp/B000BUU5TU
I use a clear fitting on the valve
https://www.etrailer.com/RV-Plumbing/Valterra/T1023.html?feed=npn&gclid=COD2svqS6dQCFQQvaQodJpkGBQ
when I dump the tanks, I hook the regular water hose to the flush valve and turn it on and open the valve and drain the tank. Then I close the valve, and let the tornado rinse the tank while the gray water is dumping. Then I switch back to the black tank. I'll close the black tank 2 or 3 times and let the water run through the tornado 6 or 8 minutes and open again. I do this until I see clear water coming from the tank. Takes a little longer to dump, but I waited in line for my turn, and I'm the one who would have to smell mine if I didn't clean it properly, so the folks behind me can wait their turn too
when I'm done, I put a couple minutes worth of water back into the black tank with the flush valve before turning it off, cleaning up and leaving. "IT" flows downhill, but "IT" needs plenty of water to flow. If there's no line behind me, I'll go inside and put a
scoop of laundry detergent, or someone above mentioned dawn dishwashing liquid, and a cap of calgon water softener liquid. Then the water sloshing around in the tank on the drive home and to the next campground sloshes around and cleans the tank good on the inside.
also, I will suggest google the 'geo method' (basically what I just described above, but more detailed) and you'll find that doing this keeps your tanks clean which will eliminate any odor.
last thing, make sure you have water on top of the flush valve in the toilet, as that works the same way the traps under the sinks do, the water in there blocks the odors. Make sure you run some water in your sinks occasionally if you don't use them, as the water in the traps evaporates, and lets the odors from the gray tank through, and that can be just about as nasty smelling as anything