Personally I just used a storage tub and then once its saturated I put it in a Aero pot (fabric pot) and then rinse it, simple and works great. I'm not to sure about the bathtub, I guess it would be OK if you disinfected it and rinsed it well but I just foresee problems with the drain clogging, IDK if it works let us know. Just FYI; If the coco your using needs to be rinsed, which is the case with most, make sure to rinse it well, VERY WELL, this is because immediately after the coco nuts are harvested they are thrown in a netted off section of the ocean to soften the coir/husk for easy removal, this leaves the coir/husk laden with salts and other foreign particles that if not rinsed off/out will burn roots and kill plants, this happened to me so I can say for sure this is a fact. Good luck and keep us posted.