You might try looking in the 12 volt Distribution Panel on the outside. Ours is located in the pax side compartment just fwd of the entrance door. The square cover (hopefully) will have fuse assignment listed on a placard on it's backside...ours is listed as position 1 - 8 and is a 20 amp fuse.
If your fuse is good(checked with an VOM), more than likely it'll be the pump solenoid or it's valve...they are both subject to seizing due to moisture.
Jan and Bob