a pint of beer per pound sounds like a reasonable equation

 

My pints of beer always end up weightless.

 

Indeed its all about the weight.

Just to add, at 03:20 in my video I said I syphoned the tank, which was fairly empty, but I wasn't sure how "low" I dare go - i think I was just too chicken!

BTW gas in the UK is around $6.5 and we're charged for recovery if the tank is on empty.

I put the drained gas in my lawn mower