Empty the butane and oil mixture into a small bowl or another container. Do this in a well-ventilated area, as the butane gas will be dissipating into the air.
Heat water and place it in a bowl large enough to hold the water and the container of oil and butane. The water does not need to be boiling, just warm.
Wait for the butane to evaporate. Butane boils at 31 degrees Fahrenheit in a nonpressurized environment, so it will evaporate on its own without the warm water, but warming the butane speeds the process. All the butane should be evaporated after about 30 minutes.