I do similar to Dutchman, in fact we have almost identical trailers. but we have a dump station at our house.
(plumbed into the sewer cleanout).
Now we do mostly dry camping, or at best places with water/electric but no sewer. couple that with a week or more at a time, often with daughter SIL, grandkids at places with no dump station. So.... the "use plenty of water" doesn't work!! We need to make the black tank last a week or more, which really isn't that hard if your carefull. But it means lots of solids, and not a huge amount of liquids in the tank.
On the road when I dump, backflush with the grey, finish dumping. At home I use the trailer built in rinser and a setup like dutchman. Only takes a few more minutes to get the majority of gunk out of the black tank. and usually the second rinse results in more TP and poop than the initial dump.
on the way home on our last stop I usually put in dose of HE liquid laundry detergent and scoop of calgon in each tank. Seems to help break up stuff as it sloshes around going down the road. Do this on both black and grey.
