It is not foolish at all. The only foolishness is on your part as you have never thought of it or come across it. A `we always do it like` this type`. As long as the washing machine pump can handle it, it is fine - that means contacting the makers. I may mean doubling up the 22mm pipe or not. This is a flat in an expensive part of of London where space is lots of money with people prepared to pay for the kitchen design they want maximising space - not at all like Northern Ireland. Using a macerator at the washing machine, ensures it would work irrespective of washing machine used - I recall some small types that were for baths only, so worth looking into. Thanks copea for that suggestion.