Red Devil TSP/90 is (according to the MSDS) 100% sodium metasilicate. I get the 4 lb bags for $15 on Amazon. Been using it for 3 years so far in my homebrew PBW and I've never had an issue. I mix large batches, as I tend to use PBW in the dishwasher, too. Great for saponifying large amounts of...
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...