ptfe tape is not a good repair if you cant find washers for drain off tap at diy shop just buy a new drain off and take the washer out they are dirt cheap. the corect washers are very thin compared to a tap washer. If the drain tap is very old it may have a fibre washer. get the new washer before you open the drain tap as they often fall apart when you undo them, if the washer is not complete when you take the tap apart make sure ther is none left stuck inside this will damage the new washer.