Well that's a loaded question......

Snug as it will go without distortion...Thinner the pan, the lighter you have to go....And yes, rtv,,,I used to have blue aluminum washers that captured the o-rings so they didn't squeeze out. Problem was most fittings weren't long enough to use them most of the time.. Went to the copper washer captured style 0-rings....and lots of rtv before a drop of oil goes in...

My new setup by Billet Fab uses a static pickup and AN16 welded fitting....no leaky washers...