When you operate the washers you can hear the pump run instantly, it just takes a while for the water to get up to the nozzles because its all drained back down to reservoir.
I must admit I do prefer an instant squirt of water on the screen before the wipers move, I dont like the wipers rubbing on a dry dirty screen. So I added a couple of simple cheap one way valves to each windscreen washer nozzle to stop the water draining back. Instant squirt ! Much better.
Doesn't affect the wash on the headlights at all, this has its own pump with no drain back as its virtually level with the water reservoir anyway. This pump only works when the headlights are in use.