Originally Posted by dutchoven
I keep a 5-gallon bucket of solution on hand; 3.75 oz (weight) PBW per 5 gallons. I soak my carboys half to 3/4 full and swish it around every now and again.
Keeping solution around for more than a few hours at most isn't a good idea. PBW is comprised of sodium metasilicate and sodium percarbonate (oxiclean). Metasilicate will etch glass, but retains its cleaning power for a long time in solution (so it'll be fine in a plastic bucket). The percarbonate is another matter; once dissolved in water it will generate hydrogen peroxide, which will continue to decompose. The cleaning performance will be dramatically reduced after a few hours, as the peroxides help to oxidize and break up organic residue.
As for the concentration to use, the directions say 1 to 2 fluid ounces per gallon; 2 tablespoons (tbsp, not tsp) make 1 ounce -- so it calls for 2-4 tablespoons per gallon.