At the bottom of a hole.

Ah, the end of an excellent weekend and back to the less romantic day-to-day practicalities of owning a B&B - especially one whose building incorporates a significant number of, um, Interesting Features..

One might assume that water is supposed to drain from the mixed-water (some rainwater, some bathwater - don't ask) downpipe on the right, into the corresponding branch in the wastewater drain.

It doesn't.  Currently it doesn't drain anywhere, nor does it seem to have a hole through which it is supposed to.  

When I eventually get things moving it appears in the other arm of the drain.  I conclude that whoever installed these had his boy scout knotting homework on his mind at the time.