Don't wait! Had a different problem with my Blackwater tank on a different trailer not emptying completely - and not realizing it! I pulled up to the dump station several times, and it would empty out some, so I was fat, dumb and happy. The monitoring lights showed it about 1/2 full, but we all know how unreliable the lights are anyway. It was pretty hot this past summer, and whew! Went to use the trailer, and it was ripe - but thought that was just because it had set in the heat. Well, went on a trip, and the Black water tank filled up real fast - to the point we couldn't flush the toilet, fortunately on the last day.
Went to the dumpstation, and it didn't dump, even though it was full. So, if anyone has watched the Robin William's movie "RV", you know the situation. Had to unplug the blockage and my wife ran about 20 trips with a bucket of water to flush out all the waste.
I would suggest as "Big Smokey" said, add plenty of water, and flush the toilet often to add additional water. That was our biggest problem, we were trying to be too frugal adding water to the Black water tank, and the TP didn't dissolve completely, making the blockage.
Ed & Mary
2011 Sunset Trails 24RB
2012 Dodge RAM 1500 5.7Hemi