Problem with rear window washer

I have a problem with the rear window washer on my E46 touring, and I
was hoping that someone using this fourm might have some input on how
to fix it.

When i start the car with the back wiper in the "off" position, the
wiper starts automatically and washing fluid comes out. it continues
doing this until i switch the wiper into the "on" position (the wiper
still runs, but no fluid comes out).

Has anyone experienced a similar problem?

Thanks for any input!