Regarding the anti-drain back valves in oil filters:
I had heard about these sophisticated devices for years. To satisfy my curiosity of exactly how these valves work I bought and cut open several brands of oil filters. AC, Motorcraft, Fram, STP, Baldwin, and several other brands were included when I did this.
It turns out that the "valve" in these filters works on the same principle that the flapper works on in the tank on your toilet. In other words, in a toilet tank, the weight of the water pushes down on the flapper and keeps the tank full until you raise the flapper by flushing.
I have learned that almost every automotive oil filter you buy has an antidrainback valve, the exceptions being filters that are on the market for applications from the 70s and early 80s and prior.
Take any filter and look in the smaller holes on the base. If you see black rubber, in most cases that is the drainback valve.
How good does this valve seal? ? ?
It's easy to major on minors. My experience tells me that a most name brand filters (**** being the main exception) and most private label filters will provide the average user with all the filtering capacity he needs. (Assuming the proper application of the filter, of course.)
By the way, I buy and install several thousand oil filters a month, so I have more than a passing interest in them.
Hope this helps and is more than useless trivia.
Steve