Matthew McCoul wrote:
Now, if I leech the tannic acid out, then i use that water for some other purpose (watering blueberries), I feel considerably less wasteful.
This chemist smiles upon your ingenuity. Tannic acid is not an acid with an identifiable molecular structure (despite efforts to designate one specific isomer, C76H52O46, as THE tannic acid); it's just tannin that has sat around until it oxidized. Tannin and its bigger cousin lignin are what make
compost tea brown. Those big molecules, with lots and lots of double bonds have so much absorption in the UV and near UV that they have smeared their spectral absorption into the visible until they are brown. Big molecules like that are not going to be taken up by your blueberries, but they are going to be a feast for the fungi in the soil around your blueberries; which the the fungi, being nice commensal organisms, will digest and share with the blueberries.