The race gas drums end up empty. You can also buy appropriate containment skid to put the drums on, or build your own containment.
IMHO appropriate containment is a crucial part.
For the small 5-6 gallon gas cans one could make the proper size containment by cutting down a 55 gallon drum so it would hold all the volume set on a grate on top.
Note the grounding too. This has all been worked out as far as safety.