I have an old Fram canister bypass filter on my '38. Because it won't fully drain due to the hole in the stand pipe being toward the top it has a drain on the bottom with a 1/8 NPT plug. If your canister doesn't have a drain you can use a turkey baster to suck the oil out. Word of caution, buy one of your own. Wives get very upset if you use THEIR baster for that.
