Problem with window washers

Hi,



Recently bought my E46 318ci, but have noticed a bit of an issue with the Window washers.



When i pull the stalk back to clean the windscreen, a jet of water comes out of both jets, but then instantly drops to a trickle of water, i then have to repeatedly pull back on the stalk to get enough water on the windscreen to clean it.



Is it likely to be a problem with the pump or something else?



Any advice appreciated.



Thanks