I keep a bucket of star san in my basement by the swamp cooler bucket. Call me lazy but I just keep it until it's gone and make up a new 5 gallon batch. Everything that will have any contact post boil goes into it. I use my old bottling bucket since I keg now and don't need it anymore. I've never checked the ph even though I realize I probably should as a bucket can last me 3-6 months depending on how often I brew. Bottling bucket is nice because then I can hook the hose up after I've cooled the wort and push star san through my chiller. I dunk bottles in it when I bottle off tap, give a quick dunk to caps before putting on bottles, very handy bucket to have around to keep stuff sanitary.
When I empty a keg, I clean it out and then put about a quart of star san from my bucket in, seal it up and slosh it all around, then push it out through my taps. This serves to sanitize the keg, the lines, and the taps before hooking up a new keg.
For reference, I keep a tub of PBW for cleaning purposes as well.