I've got a Polo which suffered from the same problem. The screen wash pipe kept popping off a connector inside the boot. On the Polo you have to lift up the trim on the left hand side of the boot interior which reveals a couple of wiring looms and the screen wash pipe, don't know if it's the same on the Sharan. If it is the same you may have to clean the wiring loom connectors as well due to the pipe joint being directly above a wiring connector causing the screen wash to go straight into the electrics. I fitted a small clip to stop the pipe from coming loose again.
Richard
February 2008