Plumbing in a washing machine or dishwasher — how do I do the connections and drainage right?

Short answer: the appliance is easy — the PLUMBING details are what cause leaks and floods later, so get them right. On the WATER side: connect to a dedicated valved supply (its own isolation valve so you can shut it off without draining the house), don't over-tighten the hose (finger-tight plus a fraction on the seal), and check it after. On the DRAIN side: the waste hose goes into a proper standpipe/trap at the right HEIGHT with an air gap so dirty water can't back-siphon into the machine and so it drains freely without airlocking. Add a hammer arrestor if the fast-closing valve bangs the pipes. Small mistakes here — a loose hose, a drain too low or shoved too far in, no trap — are exactly what floods a kitchen at 2am.

The water side: - Own isolation valve: connect to a dedicated valved supply so you can isolate the machine alone. A quarter-turn valve you can actually reach is ideal. - Hose connections: the fill hose seals on a rubber washer — hand-tight plus a nudge, don't crank it (over-tightening splits washers/threads). Check for weeps after first use. - Water hammer: a machine's solenoid valve snaps shut fast, which can bang the pipes (water hammer); a hammer arrestor or securing loose pipes fixes it.

The drain side (where most problems start): - Standpipe + trap at the right height: the drain hose discharges into a standpipe with its own trap (stops smells) at the correct height — too low and it siphons/drains continuously, too high and the pump struggles. - Air gap / no push-fit-airtight: the hose must NOT be sealed airtight into the drain — an air gap prevents back-siphoning dirty waste water into the machine, and prevents airlocks. - Don't jam the hose deep into the waste — a common cause of siphoning.

DIY or plumber? - A confident DIYer can do a straightforward washing-machine swap onto existing correct connections. But a new installation (new supply, new standpipe, or a dishwasher tied into the sink waste) is best done by a plumber — the drain height, trap and air gap are exactly what people get wrong, and the failure mode is a flood.

Common mistake: no isolation valve, an over-tightened split hose, or a drain hose too low / jammed airtight so it siphons or smells. Get the supply, standpipe height and air gap right; for a new install, a licensed plumber sets it up so it won't leak. Anyone had a washing machine flood traced to the drain hose?