Chlorine used for short periods in moderation won't hurt the tanks. You're putting some in everytime you fill the tank with a hose.It takes very little bleach to disinfect. I use 1 teaspoon household bleach per 10 gallons - fill tank, wait 30 minutes - ideally while rolling the boat around in a sea, flush twice.
I'm also planning to experiment
with Orange TKO to clean as well as disinfect - it is non-toxic and if there's a slight remaining "orange" taste that seems better than most alternatives. I plan to dilute it well too.