This goes in the toilet tank, So how it works is you either use pool shock or hot tub chlorine pellets in the big part, then everytime it's flushed it will add chlorine to water in the tank. It has been in the tank for 2 months now and the kids bathroom smells wonderful and the toilet is clean no rust from the well water, to test it when I put it in the back of the toilet it had a rust ring around the inside and disappeared in about a week.