Turn off the 12v, open the tap and pull an inflated balloon over the end of the tap. When the air escapes out of the balloon it should blow any water left in the tap body, tube and pump back into the jerry can under the sink.
Somebody posted a while ago that you could try the pump from an inflatable awning to blow the water out. For this you would need a short length of bike innertube to make the join.
Colin