could be the hot or cold value
could be the hot or cold solonoide or could be that the water from the grey outlet is syphonning back in to the washer check where the grey hose is going to if under the sink pushed on to plastic nozzle if it is this could cause water to enter when washer is swiched off
this water will be full of waste dirty water from washing up you will need to fit a none return valve or have complete outlet replaced
pete madden
March 2007