92saturnsl2
Thread starter
Practically speaking after everything is tightened down the big flat rubber ring ends up pressing down far enough into the housing to cover the drain hole and stop oil flow through it, otherwise you'd have the same problem as if you installed the nipple filter incorrectly.
I'm confident after looking at the filter housing and one of the flat bottom filters (which ironically, I found one in my stash of filters) that there is zero chance of creating a seal over the drain hole. The raised portion extends to the hole on both sides, the rubber would have to form over the hole just right, and it's not particularly flexible. Not a chance, IMO. I'll take a photo next time I have the housing open and revisit this.