You should have the correct crush washer for your large drain plug. Only the latest version oil pans, or replacement pans, used a smaller drain plug and seal. In this case the drain plug has a 13mm head. Most importantly study the oil filter canister and seal information on this site to make sure all the rubber seals are in place inside the filter housing. This is critical since often times the upper filter seal (inside the housing) is missing. If this is the case your oil is not getting filtered!!