Goat's milk soap huh! Easier to milk a goat than a grizzly? Ok,ok!
I believe that any soap you choose will do. We use Dawn for dishes.
I like to leave a little water in both tanks occasionally and add a cup of liquid tide, then as I drive to the next stop things get washed around and when I dump at the next stop and the tanks are cleaner. (That is only a bubble machine blowing from my roof vents.)
Yes, those pesky indicators work when and if they please. The shower is full of water honey, says the gray tank needs to be emptied. After a while you learn to listen to the black tank and know when it is ready to dump.
2001 Ford F-350 Super Duty CC Dually, 7.3 Diesel
2011 Cedar Creek 36CKTS Touring Edition
Full body paint, Cummins Onan 5500LP, Andersen Ultimate Hitch
We were on the road to ALASKA May 6, home Sept. 13, 2016. 23 states, 3 Canadian Provinces, up to the Arctic Circle, 17,300 miles, 131 days on the road. 1 flat tire, 4 oil changes. What a beautiful trip!