Thetford Fresh Water Tank Sanitizer

We sell it at the store and haven't had any complaints that it doesn't work or it's not worth the price. I just use 1/4 cup bleach for every 15 gallons of water, fill up the water tank, run that mix through the pipes and let it sit for a couple of hours. Then I drain and refill the water tank and run water through the fixtures until I can no long smell bleach. I do this a couple of times a year.