Originally Posted by Kaadk
I don't know. I haven't had much luck with the toilet flushing when the kids put in a large volume of water. Been more like "Honey, get the mop and a plunger!".
Just pumping into the bowl would probably overflow it. If you were to actually push the end of the hose down into the through the base of the toilet you can pump into it without issue. Don't ask...
A better solution would be a tie in in the basement or crawl space - like a threaded cleanout fitting. You could take the plug out and get some pvc parts to either reduce back to a hose fitting, or just leave an open stand pipe with a U-trap to pump into. Black first, then flush everything with the gray. Then you can just unroll a hose from the trailer to the house whenever you need to empty the tanks. Just make sure you pump with a macerator pump.