another q: should I expect water **not** to flow back through the Gulper?
That is, the Gulper pumps out the bath, some water sits in the hose between the pump and the through hull. I think TheBiscuits got it right in that the drain from the sink connects higher than the gulper pipe, thus filling the pipe back to the Gulper [from where the sink connection joins it]. Grey water then finds its way back through the pump, and into the pipe connecting the pump to the bath, slowly refilling the bath.
If i simply do the rotation advised, does that fix it? Or does the fact