[Zoomad75]

You probably have a worn out pump. You can buy a rebuilt kit at most parts stores. I've found on my 75 K5 that the mechanisim that drives the pump from the wiper motor can wear out over time. I've rebuilt mine a couple of times to only have it stick and pump whenever the wipers are on, or not pump at all.

I got fed up with it and swiped a bottle off of a 93 S10 Blazer with an electric pump from the junkyard. By using the wiring that controled the solonoid on the factory mechanical pump my electric pump still works with the stock switch. So from the dash it works the same, but now it pumps fluid 5 times better than the stock crap would. If I aim the squirters right I can shoot over the roof and hit the next car behind me at a stoplight.