Since your running it indoors, have you seen that little trick of taking your material, about a 1/3 to maximum 1/2 of a 5 gallon bucket at a time, and lots of water and a drill with a big paint stirrer on it you can pickup from Home Depot, Lowes or probably just about any hardware store.
Process it with the drill mixer, just like your mixing up a bucket of paint. When its thoroughly busted up, most of the dirt and other junk will be in suspension. If there is clay it will bust it up pretty good also. Then pour the muddy water out of the bucket and run the washed material through the recirculation system.
This would have to be getting rid of over 99 percent of the crap for a small amount of water, versus running it and clogging your recirculation system causing lots more work and water loss cleaning it back up allot. This could even be done on a recirculation system in the desert since you don't have to run any contaminants into the process.
I haven't personally done this, but I have seen it done and it seems pretty solid on getting the most out of recirculation system by pre-cleaning.