Our 2011 Toyota Yaris Mk2 has problems with both front and rear windscreen washers. The rear one is now barely a trickle, and the front ones seem low on power. I can hear the pump working, so I'm guessing that there's a blockage in a pipe or that the pump is not working properly. Is there anything I can do to diagnose (or even fix) the problem, or am I looking at an expensive garage visit?