Replacement may not be needed, Sometimes after a period of non-use it will stick, Simply pressing the center button will clear it (Remove screen washer, depress center button, replace screen washer and try again.
WARNING: Sometimes pressing that button will break it, but since you are already planing on replacing, no loss there.
Check with the on-board water pump on too.
On my coach is a 3-way vavle in one position (normal) it feeds city water to the "House" systems (Sinks, toilet, shower). In the other (FILL) it feeds city water to the fresh water storage tank.
Home is where I park it!