Draining: Pumps, Filters and Siphons

Open the pump filter of a washing machine that's a few years old and you'll find a small collection: coins, hair grips, buttons, the odd bra underwire, a baby's sock. They end up there for a reason. At the end of every wash, waste water runs from the bottom of the tub into a sump, through the pump filter, a removable trap on the front of many machines, and into the drain pump. The pump's impeller, a small plastic paddle wheel, flings the water up the drain hose and out to the household waste pipe.

The filter is there to stop anything hard reaching that paddle wheel. When it fills up, water drains slowly or not at all. But the filter isn't the only place draining goes wrong. The hose, and how it's fitted, matter just as much. And a hum from the pump doesn't prove the paddle wheel is turning or the water is moving.