If I want to drill and tap a 1/8 NPT hole in an oil filter take off for a gauge sender what sort of initial hole is required and then how is the thread best cut?

You need a decent thread cut through the whole depth of the hole. I am guessing you can over do this as the tap is tapered and so if you go too deep it will ream the hole to the diameter of the widest / deepest part of the tap.

What is the best size hole and any tips on cutting the tapered thread without going oversize but ensuring that a good thread is achieved throughout the taper.

Bit of a waffle but never cut a tapered thread Might be worrying about nothing but any tips welcome.

What bit / tap do you reccomend?