I do this two different ways. The simple way is to fill a large panning tub or 55 gallon plastic drum cut in half sideways and places the clays in there and blast it with water while stirring it up. Let it settle for a minute and then dump the dirty water into another container and let sit for a minute, and then pour off the access, and repeat. You may end up doing this ten times and going through a lot of water.

The other way to do it is to get a 7 gallon bucket and cut a hole near the top large enough for a 2 inch PVC pipe, then attach a 6"-8" long PVC pipe in the hole and place a 5 gallon bucket below it. Add your clays only about 1/3 full on the 7 gallon bucket and spray with water and stir, and stir, and make sure your hose is spraying the bottom. As the water rises to the top the fine gold and sands will go into the 5 gallon bucket through the pipe and have time to settle to the bottom while you keep stirring and adding water. When your 5 gallon bucket feels up pour off the water, and you might have to repeat a few times depending on how loamy the soil is. But when the 7 gallon bucket is showing clear water and your fines left at the bottom put them in a second bucket to be worked or panned, they should be clean at this point. At some point depending on how much heavies you have at the bottom of the 5 gallon bucket you may want to rinse them a few times, but they should be mostly clean and then you just add them to the bucket to be worked or panned.

Busting up clay for panning sucks I know, and I dont think there is anyway to do it without a lot of water so we always try to get our material as clean as possible at the river.

Something I have never tried but might be worth a try is dumping muriatic acid into bucket, just make sure you are wearing safety gear and add the acid slowly, all the organics are going to foam like crazy and you had best be outside and have a source of water nearby when you do it. Working with acid can be extremely dangerous so you might want to start with a small amount as a trial, and when I say small I mean one to two clumps of clay in a acid proof container you can buy at True Value Hardware.