In order to get yeast and trub to easly slide out the cone needs to be at an angle of 60 degrees or better, although those nice plastic induction tanks are about 57 degrees and they seem to work well. A plastic water bottle or better bottle would be nowhere near that. You'd just have a ton of junk sitting on the shoulders and clouding up your beer as you racked, to say nothing of the oxygen permeability problem.
I can't be arsed to keep up this list of what's in the fermenters, but hey, check out the cool brewery I'm opening up!
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