Spend the $ s and get a good one that you can pull by hand - the one I have traps air so when you get ready to disconnect you push the red button that shows is full down and allow rest of stuff in pipe to go into tote....then hand pull it to dump.....I only use mine for grey water, but can do black in a pinch.
If you don t follow instruction you can have a mess with any of them...guess that is why shower is right next to dump....LOL.....I can use mine on a ball if in mountains where there are up hills to pull when full......mine is 18 gallon.