Keth - you can get tergitol much much cheaper than that at thechemistrystore.com. As with how it works, yes it makes the stuff hold much better on the sides of a house - but even on flat sections, it has this amazing ability to remove the need for brushing. If you use it with just bleach, ok - or just use bleach with TSP - again ok. But bleach with tsp and tergitol - man oh man.
-Dan