I'm not giving advice (except I wouldn't recommend it!) but know that "in the good ol' days" the CAT dealership in Cheyenne would weld quik fuel couplers into diesel tanks on heavy equipment.  They simply drained the fuel down to below where the coupler needed to be.  I WILL NOT DO IT.

I have welded a couple of 140 gallon storage tanks by filling them with pickup engine exhaust.  The last one it did, I shut the engine off after I got started welding.  I noticed slight "popping" and then noticed that the bung hole on the other end was popping out puffs with flame.  I restarted the pick and left it running until I finished the job.  I'm not anxious to weld on any more fuel tanks.

I spent 3-4 hours seating a tubeless tractor tire in the field today, considered ether but decided the risk was not worth it.  I've done it but have heard the horror stories since.  We finally got it with bead grease, strap winch and much patience- cheata tank didn't help.  Once we got the tractor to the shop and repaired the tire, the big compressor made it a 2 minute job.

Life is too precious to cut corners.