My new Drain Plug
So I go to the Local Auto Part store. (Lordco Auto Parts - Home Page
which is suppose to be BC's largest auto parts chain)
Me: "I was wondering if you have a Transmission Drain Plug for a Subaru Forester. It is an M20 x 1.5."
Parts Guy: "What is the make and year?"
Me: "Subaru Forester, an 2007."
Parts Guy after looking on his computer: "The drain plug size isn't in the computer. You'd have to find out the size from the Dealer."
Me: "But I know the size. It is an M20 with a 1.5 mm Thread pitch."
Parts Guy: "That doesn't matter."
Me: "What do you mean that doesn't matter?!?"
Parts Guy: "They don't make Drain Plugs that big. An M20 would be huge."
Me: "...well that is the size it is suppose to be. Could you check to see what you have?"
Parts Guy walks off and comes back a 2 minutes later: "This is the biggest we have."
Me: "This it is. It says right here Subaru Oil/Transmission Drain Plug. It even says M20 x 1.5."
Parts Guy: "Oh."
Anyways, the shop at work did have the 1/8 NPT tap. So I did the drilling and tapping myself. It is ever so slightly off center, but I am not machinist.
I tapped about 1/3, I didn't want to go too deep and over enlarge the Taper of the thread. A good thing because I nearly bottomed out the sender when it came time to cinch it down. I also enlarged 2/3rds of the hole from the other side to give clearance around the sender. The Sender unit is sealed with Teflon Tape. I am not sure how the Teflon stands up to the heat and oil, although I don't think it should matter either way with the NPT thread. The Sender has a grounding wire, so grounding will not be a problem.
Finally I put a few layers of Heat Shrink (increasing in Diameter each time), so give some protection.
So the Drain plug was $6. Drilling and Taping free. I would not recommend trying to tap an NPT if you are not confident about your taping skills. The tapered threads make it more difficult than regular threads.