Back in the early 60`s at the company that I worked for we opened one litre oil cans with a combination piercer and pourer. Told to stop using them as plating on the opener was getting into the oil. So we then opened them with any handy screwdriver without any adverse problems.
So we then later had about a twenty gallon oil dolly that we pulled about to use, this was refilled as needed from fourty four gallon oil drums.
One of us asked why did the pipe on the pump on the oil drum was short of the bottom of by some five gallons or so. Why not lower it so as to get all of the oil out out of the drum.
I forget what the answer was, there was some reason, the pipe was not ever lowered. But re shaking a one litre can before using, seems strange you have to shake a one litre, but we never shaked the twenty gallon oil dolly or the fourty four gallon oil drum.
A canditate for Snopes ??? Urban legend ???