The trommel screen sizes on dredges varied a bit. Out in the neighborhoods I poke around all the dredge tailings easily accessed are from bucket ladder operations, more often than not the sluice tailings are covered by the waste rock from the stacker. As I understand the best bet is chasing big nuggets with a detector in areas where broken up chunks of bedrock are seen in the stacker piles.
I agree, tailing piles are being reworked, but not with a MD, first of all you have to realize that they got most of the big gold, the fines are what they lost mostly, I know some have been lucky, I have spent much time in those piles from the Klondike to many places in Ak, I had better luck elsewhere...