We have been known to pull Tana's wheels up on leveling chocks or boards at a dump. Many times.
Also, note those of us that have rear kitchens, and maybe some of you others, that that galley tank is quite a ways back there, there is a LONG sewer run. Many times there is left over liquid, no matter HOW long you wait, in that sewer run. This is why CountryGuy got that extra valve. Plus with that extra valve we can equalize the gray and galley when need be.
Agree fully, that dump stations are usually NOT level, cannot tell you how many, (LOTS), that are actually "tipped" the wrong way, away from the dump/sewer hole. Now, THAT is really irritating.
