Wittenham

ah yes, that is another way to screw this up. The shower tray is a small bath tub, so i expect it will be noticed, but one more thing to think about. Thanks.

thanks Alan, is the danger that the valve is left open? In which case, the tub fills up like before, so that is ok. Or that it is left closed and the pump turned on, and it ?? [burns itself out?] trying to suck past the NRV? I like the safety tag idea!

now that i have had a good look at it... is another option to fix this to put a piece of kit in the drain pipe [a stopcock?] between the tub drain and the pump. Turn it off when not pumping out the bathtub, back on for whenever the tub is being drained?

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

A basin does share the fitting. It looks clear, but I will do a proper dismantle in daylight. as always, thanks all for the quick and quality information.

as per title, a Whale Gulper empties out the tub, and then over a day or so, it slowly comes back. Not to the same level, though. Am I right to assume something awry with the pump? I can see water dribbling out the drain hole.