The screw on cap that is on the bottom of the oil filter canister; what is it for? The cap unscrews from the bottom of the oil filter canister and there is what appears to be a port of some type. This is my first experience with an oil filter canister with replacable filter of this type. But what is puzzeling me what on the bottom of the canister. I appreciate any knowledge/help. Thanks.

i believe its for the techs at audi to drain the oil thats in the housing so when you unscrew it, oil doesnt go everywhere. i wish i had that tool because its annoying. if you still havent done the oil change id recommend you remove both shields. it gives you easier access to the filter. the drain plug is a 19 mil. and the filter is a 36 i believe..

This allows the oil to drain out of the canister. It also releases the fluid lock so that the rest of the oil can drain into the pan. Proceed from there.