Use in tank electric fuel pump to empty tank?

I , too, have done it many times. As others have said - only into a gas can or two. I will add two things - you may want to make a ground wire from the hose to the tank, to keep static electricity at bay, and at the least, where the hose enters the can, seal it with a rag. The raw gas being pumped in under pressure, will also cause vapor to form, and will quickly fill a garage to a point where the low/high explosive limits could be reached. Simply sealing off the opening by stuffing a rag around it, will greatly reduce that.