I have a small Rule submersible inline pump that I use for odd jobs.
12 V 500GPH Model RWB2621
Just slip on a bit of garden hose on the discharge, and plug it into a 12V outlet. The filter comes off the suction side giving access to a hose barb on both ends if required.
I've used it mainly for water, but also to empty my old fuel tanks. Works great so far.