Anymore, I only use Star San to sanitize bottles for packaging beer in for competitions. For general sanitizing of my fermenters and plate chiller assembly, I use Saniclean because it doesn't foam like Star San. I can keep it around for a couple months in a Gott cooler. If the temp gets down to the 50's in my brewery, there will be some of the solution that tends to precipitate out. I asked Five Star about this and they said it would not degrade the effectiveness of the solution. Just make sure if you store either that you check the pH from time to time to insure that it stays below 3.0.
I just dump down teh drain when finished with them or they lose their effectiveness. It doesn't seem to bother my septic system.