TSP (trisodium phosphate) is a cleaner that is usually used to clean drywall before painting. The book that comes with the Brewer's Best kit suggests using a mixture of bleach and TSP to clean your bottles. I got some from the hardware store and it seems to work ok. I eventually ended up switching to oxiclean free and now my TSP is just sitting under the sink unused.
The way I understand it PBW is essentially a combo of the active ingredient in Oxyclean and sodium metasilicate which is TSP-90 at a ratio of 70 oxy 30 tsp
use only TSP-90 as it is 100% sodium metasilicate