Good stuff. I'm looking to wash, claybar, seal, glaze, and wax my car this coming weekend. I also use several sponges and use two buckets when when washing the car.
I use one bucket (plain water, no soap) to put the sponges in to rinse them out. It doesn't make any sense to take the dirty sponge and dump it in the soapy water. All you're doing is removing grime and putting it back on the car
Obviously the second bucket is just for soapy water.
I use two sponges (sometimes 3 depending on the job). I use one to clean my wheels and another one to wash the body of the car. Once again, using the same sponge for an entire car is a self defeating proposition. I clean the wheels first as they tend to be the dirtiest and it's also to prevent the grime from the wheels getting on the body of the car.
I used to use Black Magic stuff, but since SEMA this past year I've switched over to Mothers.