so, I am going to drop my metal auxillary gas tank in my 40 and have it cleaned and lined and decided to also put a sending unit in it while I have it out and before I have it lined. as it apears to have no hole for a sending unit due to age, what is the safest way to do this without blowing yourself up? any safe rule of thumb for how many days to let it sit until fumes are surely gone after I drain? what about sparks and residual combustible fuel/sludge on walls when you drill? any way to suggest (or facilitate) airing/drying it out or before I cut the hole using what one would have in a home shop? any previous experience and plan of action for doing this safely would be much appreciated.