Originally Posted by Ray,IN
Some RV manufacturers used to plumb their units this way (bathroom sink into black tank) to insure adequate water was added to the black tank to reduce the possibility of plugging the tank with solids. Obviously yours is one of these manufacturers.
If you are handy with plumbing it would be feasible to re-route the sink drain to the grey tank_but, usually the grey tank fills much faster than the black tank anyway.
We camped last week and I did another verification check and no longer think that's the case. I had GREAT water pressure at the site so I connected the elbow flusher I bought and flushed the black tank several times and did get a lot of solid waste out of it. I never did get it to run perfectly clear or even stop spitting solids but I had to do a lot of flushing. Going out again soon and will repeat. I am starting to think I was right in thinking that the former owner had the black dump open (and I know he had it permanently plumbed to drain with PVC pipe) and fouled the tank thinking it was all going right down the drain.
I have also in the past dumped a 20 lb bag of ice down the toilet just before taking off on the road to slosh around and break up solids. I will do that a few times too.