I use a Thumler's model B, it's large enough to do a decent load of coins and the tumbler is well-built. It's worth what you pay for it. As far as tumbling, I put three big handfuls of coins in, then fill the rest of the tumbler about 2/3 full with aquarium gravel. You can get that at Walmart cheap. Add a squirt of dish detergent. Do not mix clad with pennies, your clad will come out looking copper. I run the tumbler about 12 hours, then check it. The water should be nasty, sometimes the coins still have a greasy buildup on them. I change the water, shoot in a bit of 409 and run it another hour, most of the clad comes out shiny after that. You will have some that doesn't come clean no matter what. For pennies only, add 1tbsp of cream of tarter (polishes them) and run 8-10 hours. Again, some will not come clean. Be sure to cull the copper-plated zincs (1983 and later) that have any corrosion on them, the corrosion pits will only leech black onto your other coins. Give this a try, experiment a little, and you should be able to turn 95% of your clad back into the bank cleaned. Some banks take it dirty, mine does not. It has to be clean enough to be accepted by the big expensive coin counters they use.