I find an appropriately sized plastic containder, Bourgest pan, etc. I put my target piece of meat in. (I wish marbles were cheaper.) If necessary I fill up some of the air space with biggish non-reactive objects. (Biggish and irregularly shaped so that these pieces don't cover significant amounts of meat.) I then fill up with WATER and determine whether or not I need a weight on top of the meat. Make adjustment. Pour off water into measuring jug. Measure. Then go back 50 years and recall my algebra. Consult recipe. Recalculate ingredients for the amount of water in the jug. Alloiw a bit extra for loss by heating and boiling brine. Add ingredients to water. Boil. Cool. I don't see any need to reuse brine, given this method. There isn't that much to discard.
Those who know more than I might assert that by limiting the amount of brine in the vessel, I an limiting the amount of cure that can get into the meat. Works for me.