I use cheap toliet bowl cleaner. Clean the nickel clad separate from pennies and place all
the coins in a old bowl and just add enough cleaner to cover them.
You will want to do this outside and with rubber gloves.
Just grab the bowl and swirl the cleaner around the coins for about a minute, empty cleaner from bowl, rinse coins well with water and let dry.
Now, most will come out looking chalky ..just grab a soft brissel copper wire brush and give them a few strokes front and back and they will
clean up pretty well. This method will pit the surface of the coins just slightly, so make sure its just junk clad and check them for any mint errors
before cleaning them.
I use this method and can clean about 6 bucks in clad in just a few minutes...the cleaner can be bought at any Dollar General store for a buck or two.