maybe try more foreplay
failing that, stick a pin in the jet to make sure its clear, if still no result then your going to need to get your mits on a bike pump and blow air at pressure through the tube behind the jet to unblock
aim is never to let you washer fluid get too low so it doesnt suck dregs through the pipework, if the jet is fubar'd btw they arent expensive and readily available from your vw parts dept