http://www.allelectronics.com/make-a-store/item/STS-80/DPDT-ON-OFF-ON-MOMENTARY-TOGGLE-SWITCH/1.html

Two of my three two tank cars have the loop behind the filter. MY 84 is return to tank. But my last old Mercedes 300d had it looped in front of the filter.

My grease is really clean. And running multiple passes on the filter is not bad. I change veg fuel filter at every oil change anyway, then it is never an issue.