On the 3 engines with bypass filters that are in my shop right now, all of them have the return line at the bottom of the filter canister, with pressurized oil going into the side of the housing. If the engine sits for several days without being run, practically all the oil should drain back into the pan. A very badly clogged filter would keep some oil in the canister, but a clean filter element should let the oil drain back pretty quickly. The restrictor for a spin-on filter should be about 1/16" in diameter, and it can go into either the pressure or return line.
Jerry
