You can pick up a submersible pump from Harbor Freight for really cheap. I use one as a recirculating pump in my wort chiller for homebrewing. You could stick the pump at the bottom of the tank with a bit of extra hose, or even a spray bar causing the water to recirculate in the tank. Added with the shower head at the bottom of the tank set to very low causing a very slow spill over, I'd think you would have a very decent home made washer.