This is the recipe I loosely use.

Here is the recipe I was given when I bought my tumbler. Mine is a Thumbler's Tumbler.
4 squirts of Lemi Shine
4 squirts of Liquid Sun OXYgen (I used Dawn)
1 tablespoon of cream of tartar (yes the cooking powder). Makes the brass very slick.

1-2 lbs of brass or steel pins

I filled my tumbler ¾ full, added the pins then brass.

If you tumble for 2 hours or so, it'll look like new.

Good look.

There are 2 rules to success:

1. Never tell everything that you know.