In order to save kitchen space, I was looking at fitting a washing
machine in an upstairs hall cupboard. The drain would have to run under
the hall and across the bathroom in the suspended floor space. The
joists run with the drain route, so no problem getting the drain under
the floor. The water is pumped by the washing machine and using a clamp
on non-return valve connector on the drain pipe I don't see any
problems. Does the drain need a strong fall to it?

The pump of the washing machine isn't intended for long tortuous runs like
this. It should empty into a trap near the machine.

However, all is not lost. You can buy pumps which are intended for this
purpose. The Saniflo range would not be suitable as they do not allow a
vertical run at the end, only at the beginning. However, a Sanisplit K2
(different company) should do the trick. They're not cheap, though. The
other alternative is to run by gravity to the base of the vertical run and
then install a Sanivite at that point, rather than near to the washing
machine. However, it won't be any cheaper and probably a whole lot less
convenient.

Christian.