"Guy King" wrote in message
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Another point is that can the drain pipe be in a 'U' shape? The
pipe drops from the washing machine, under the floor and then rises up
and connects onto the 110mm WC pipe. Water will be trapped in this
pipe.

Washing machine pipes are always full of water.

I really think you're making this more complicated than it needs to be.
If you're in any doubt about whether the washing machine pump will cope,
make a mock-up with a length of 32mm waste pipe laid on the floor and
you'll see it'll cope no trouble.

Most washing machine drain pipes I find that don't have a good fall, or are
straight, end up being fully or partially blocked with gunge.

The best is gravity of course, using slow bends where used. Using a Sanilav
or Sanisplit pump is the last resort but should work well. Even the gravity
fall pipe I would have accessible rodding points at every opportunity. One
could be at the washing machine end under the floor of the cupboard the
washing machine is to go. Have an easily removable trap. I would use solvent
weld pipe and fittings. I would also occasionally use Mr Muscle drain
unblocker down the drain pipe to burn away any gunge.

If using 22mm pipe and a Sanilav pump I would also put rodding points in, or
have compression joints in the loft to easily break the pipe and get a rod
in.