What size tread, Turbo Oil Drain tube

[JUSTAV6]

I have a 4.1 block and I need to drill the hole for the turbo drain tube ,, So what will I need?? What size bit and tap what tread,
Thanks for any and all help
Seneca Lafler,

 

[49-blues]

I did mine with a 1/2" pipe thread,drill size just under that.