Okay so the brew pot I acquired on craigslist holds 15 gallons at the brim. I bought the biggest grainbag AHS had...is the pot too big for a 5 gal BIAB? I know I'll start the boil with 7.5 gal, but that looks like barely any at the bottom of this pot. Also, If I go 10 gal BIAB that will be 12...