Clean nozzle with a pin, filter possibly under the jet head find pipe pull off check under the jet piece for gunge poke out with stiff piece of wire reassemble.
(lack of pressure,I remember years ago car makers used to put a one way valve in the line to prevent water running back this made the washer work straight away.if none now fitted water has to dragged all the way from the bottle to the jet(maybe 12 -18ft) away before it can pressure the line when the pump STOPS water drains back.
wirecutterman, January 2008