We had a bloke that used to go around putting 2" outlets on diesel storage tanks. Tank had to be FULL of diesel, he would the weld a short piece of 2" threaded pipe into the base of the tank. Then he would put a tap on with a cap on the other end with a hole saw on a shaft that fitted inside the tap (shaft came out thru small neat hole in cap) . He would then drill the hole thru the tank, pull the holesaw back, turn the tap off, then unscrew the cap and bingo, one high flow fuel tap.

This all worked great... until one day he SOMEHOW, and I can't think for the life of me think HOW, mistakenly tried this on a tank full of PETROL! He is no longer with us. Yes this is a true story. I've done this on one of our diesel (1000 gal) tanks this way and am still here, but BOY was I nervous! I was told by our local bulk fuel supplier that this is safe AS LONG AS the tank has NEVER been used for Petrol, but don't think I'll do another one all the same.

Theory is that the diesel simply can't get hot enough to explode. Petrol on the other hand......