I still do what worked 50 years ago in gas station lube bays. Spill gasoline on the floor. Push it around with a broom. Spill about a gallon (enough for a 20x20 garage) of burnt rice hull ash (available at NAPA). Push ash with broom and cover entire floor. Let sit for about 5-10 minutes and then sweep it all up. Floor comes out looking clean and slightly white form the rice hulls. Re-use old rice hulls at least 20 more times before tossing away.

Ivan Vegvary (working from the same bag of hulls for 25± years now)