tank drain valve question

[Paul B]

How far should I be able to screw the drain valve into the drain valve flange? I have tried both valves and flanges and applied a small amount of Lubriplate. The deepest I can get the valves still has half the threads remaining outside of the flange. The drawings show the drain valve nut to be flush or nearly so with the flange. I am afraid that if I use any more force, something will break!!

I am thinking I should find the appropriate tap and run it through the flanges. Is this acceptable and what would this tap size be?

[Mel]

These are pipe threads. If you have 1/2 the threads in, you are good.

You don't want the threads to stick up inside the tank. This has to be a "low" point.

[Skyflyer]

Mine did the same but seal well without leaks.

[terrye]

The size is 1/8" NPT. Normally pipe threads are tightened from 1/2 to 1-1/2 turns from hand tight. On aluminum I would go with 1/2 turn. I would use FuelLube or EZ-Turn (from Aircraft Spruce) to lubricate the threads, prevent leaks and allow for removal.