its all run off the same reservoir. the pump has a 2 way valve which directs the screen wash to front of back. check the pipes for blockages. worst case is u need a new pump. try removing the rear jet (remove the 3rd brake light and pop it out, disconnect the jet and see if water comes out the pipe, if it does, then the jet is blocked so try unblock it or replace. if still nothing, ur looking at pipe/pump.