I've read about using a tumbler with aquarium gravel. One post said to use a "squirt of detergent". My question is: do you put water in the tumbler too?
Yes you also add water. Personally, I use liquid dishwashing detergent. I've tried several things but keep going back to liquid dishwashing detergent. You'll be surprised at how they turn out. Just don't mix the copper/zinc with the clad.
To much water and soap while tumbling makes huge soap bubbles. How much of each of the coins, soap, water and gravel, depends on the size and kind of tumbler. Experment. I make mine like a slurry,
Why wouldn't you just dump your uncleaned clad into a coin counting machine? In three year, there are only a handful of coins that get rejected, and usually then are nearly disintegrated pennies - those you could tumble all day and they'd still be falling apart.