The message
from "Sparks" contains these words:

The top of the hump would need to be at least the hose's width higher than
the highest point the water get's to in the machine, so I very much doubt a
couple of inches will work!

Ah, sorry, you're quite right. I forgot all about keeping the water in
during the wash and was just thinking about keeping a waterseal after
emptying.

--
Skipweasel
Pay no attention to that man behind the curtain.