RV Repair: Toilet odor, and not holding water., roof vent, flat blade

Question
 Darren, I have a '99 coachmen futura lite 246TB. Just lately, an awful odor has been coming out of the black tank, or at least that is where I think it is coming from. The toilet will not hold water in the bowl any longer either. When I dump the tanks, I always run fresh water through the tank via a water jet attachment that hooks up on the dump end of the valve. When I'm done flushing the tank, I run water in the tank until it comes past the water going in, and then shut the valve. then I put a bottle of campochem in the holding tank. I think that's the name of the stuff I buy at Walmart. Any help you could give would be greatly appreciated.

 Sincerely,
 Charlie Sparks

Answer
Charlie,
        I believe you have actually answered your own question.  The water in the bowl actually serves as a barrier to keep the odor from coming back into the trailer.  This is necessary since there isn't any kind of p-trap on the drain.  There may be some tissue caught in the seal where the mechanism slides back and forth not letting it close and seal properly.  Thetford makes a tool for cleaning this out, but it is essentially a flat blade screwdriver with about an inch bent 90 degrees at the tip.  To help clean the tank out further you might try putting about a third of a tank of water in it before you take it for your next trip.  It will slosh around in the tank and when you get the trailer hooked up you can drain it and start from there.  The only other thing you might check is the roof vent for the black tank.  If it becomes clogged it could cause an odor in the unit.  I hope this helps.

Darren