I do that when there is not a better alternative, but it doesn't have enough flow to do a very good job (I guess because of the small diameter hose and therefore diminished volume/flow). A direct connection with a 5/8" hose at the dump station does a much better job of cleaning the black tank. When there is not a hose connection at the dump station, it's better than nothing. I try to scope out the dump station while I'm camping and if I see it doesn't have a hose connection, I get an extra third tank in my fresh water tank while at my campsite.
I wouldn't think hot water would make any difference.
Amateur Radio WA4GIY
2015 Montana High Country 305RL
2013 RAM 3500 4x4, crew cab, long bed, 6.7 CTD, Aisin trans.
CGVW 20460 Lbs.