Which pump is it?
There are several Graupner Geared pumps with different arrangements.
Generally though, geared pumps are self-priming and reversible.
So shove on a couple of lengths of pipe, connect a battery and try a test with a bowl of water.
The pumps use brushed motors (usually ~360-380 size) so they need suppression of brush sparks to reduce potential RF interference.
You don't need to buy an expensive filter from Graupner.
Probably not available anymore anyway.
All you need are 3 capacitors; 2 x 10nF (=0.1µF) and 1x47nF (=0.47µF), connected as shown in the attached pic. The numbers in brackets are the markings on the capacitors.
Correct type is flat ceramic.
Many model suppliers sell Suppression Sets of the three capacitors, e.g. Krick.
DO NOT USE ELECTROLYTIC CAPACITORS, i.e. marked with + and - leads.
They can go 'POP' 💥 if reverse connected😮
Cheers, Doug 😎