Aha! You've actually got it, even though you don't think you do! Good going.
A fresh tank has the components in the maker's intended proportions. The components are depleted over a 2 week life of the tank of sauce. You put everything right by dumping and mixing up a new tank. Simple.
If you add stuff to the depleted tank, you may end up with more than the intended proportional concentration of some things and less of others. The point is, you don't KNOW what you're winding up with- unless you mix up per the maker's instructions. Not many will give you an instruction on how to 'freshen' a depleted tank of sauce.