http://home.nycap.rr.com/lederman/images/blockoil.jpg

If you have an AC canister filter, the inlet/outlet ports are labelled. Different types of canisters had the inlet/outlet ports at different locations.

The following AC filter has inlet on the side of the canister and outlet at the bottom. The filter drains when the engine stops. The inlet fitting has an adapter for the oil pressure gauge.

http://home.nycap.rr.com/lederman/images/54oilfilter.jpg

Tim