http://www.stovebolt.com/techtips/engines/oil%20filters/index.html#60Some types of bypass filters drain back into the pan all the way to the bottom.
Some have a drain-hole near the top of the center tube inside the canister.
Some have a drain plug at the bottom of the canister-body to drain old oil might be in the canister.
Some people use a siphon (turkey/juices baster) to suck out oil remaining in the canister.
When replacing the filter, some people put some new oil in the canister - to lessen the delay of oil moving through the canister. There is nothing wrong in doing this, but it is not really necessary (it is a by-pass filter).
