I would NOT wire one switch "hot" AKA run it through the key at least, and use a relay.
Way too easy to bump a "always hot" switch and now you have fuel trying to push through the needle and seat plus run the battery down.
They make toggles that are momentary one direction and "latch" the other. If you get a SPDT (single pole double throw) it will have 3 terminals. Middle is common, one terminal will be momentary, the other will be latch. Wire the two outside terminals together and run them off to the relay coil Wire the center terminal to the "ignition run" terminal of the key through a small fuse.
Fuse the main power to the relay and run the load contact to the pump Be careful you get a solid ground connection for the pump
