What I did (RV-4)
Lots of options here and some good comments. I installed a smoking airplanes 3.5 gal in my -4, however, all the systems are similar in function. I like the "self contained" set-up with pump on the tank an simple quick disconnects for the electrical and the fluid lines. There are times when I don't need to haul the hardware and the oil around, as well as for maintenance reasons. I have the "flip switch" On/Off/Momentary position mounted in the panel just forward of the throttle quadrant, and a momentary button on the throttle lever. The switch is definitely the way to go when doing a routine long burn, but button is great for a quick mosquito dusting or position puff in the pattern or gaggle join-ups.