It's not only oil that comes in those drums, it can be bulk paint, turps, chemicals,resins, stewed prunes, tomato puree, syrup, licorice all sorts. No need to lift the drum when full, the pram handles on it to drag it along by and the filler bung to fill it and the tap to take water from it, although because of it's weightyness when full a receptickle like a teacup would be useful to transfer water from it to the boats tank. A kettle can be filled directly from the drums tap on the bankside.
Indeed it is, I used to do it in the garage where I was an apprentice.