Hot Rods Flathead oil filter question

This may be a stupid question, but I haven't been able to find anything addressing it....I have a '47 Ford Tudor with a 59AB flatty, and While I have worked on lots of old cars, this is my first flathead. Am running the stock bypass oil filter. My question is: what keeps all the oil from draining out of the filter when the motor isn't running? I check the oil level before every start, and it stays at the full line, but it seems like the oil would drain from the filter housing and "over fill" the oil pan.

 

Nothing. The oil is supposed to drain back to the pan. But, the oil can only drain out if new oil is coming in.

Did you ever punch one hole in a can of tomato juice? Remember how slow it ran out, until you punched another hole to let the air in? Same idea. The oil cannot run out, unless air or oil is coming in.

You can take advantage of this when you change the filter by cracking the lid loose and letting the oil drain out before you take out the filter.

 

That makes perfect sense, thank you sir!