I'm with midnightsadie: heat the water in the barrel, raise it up, and put an ordinary ball valve on the bottom so you can "pump" it into buckets using gravitation. Most sump pumps would have a temperature limit, probably below the boiling point of water; the literature for the pump in question ought to spell it out.
Sometimes you can get big stock pots, 24 quarts or so, fairly inexpensively. One of those heated to near boiling might be more than enough hot water (when mixed with cold to make a pleasant temperature) to fill a small tub. Carrying a large hot heavy stock pot is not the easiest, however.