If draining is a concern, I suggested (a long time ago) to put a T at the pump (or anywhere at the bottom of the loop, really) that would point down: put a ball valve on it, and let it extend down through a hole at the bottom of the case.
That way, you can just prop the system up, and open the valve to drain it all.
(and please, if you're going to add nasty chemicals to your water, please dispose of the waste in an environmentally safe way!)
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