I have a T15 Hayward cell. I screw on an ABS cap onto one end, stand the whole thing upright and add the cleaning solution. After sitting for a bit I dump the contents slowly into a bucket of water to dilute the cleaner. Then I throw it into the scrub land behind my backyard. I once made the mistake of dumping it undiluted onto my lawn where the pool equipment is. This killed the grass there. Not much and it did recover but I did have an unsightly brown spot for a few weeks.
Yes I've heard of this too. If you clean your cell the old fashion way, mixing water and muriatic acid this is certainly an option. The pool volume is much greater than the amount your use to clean the cell. It's also the sort of thing people put in there pools to bring the PH level down. However, I'm lazy and buy the pre-mixed cleaner solution which is pink in color. I don't want that in my pool.