I use a quarter of a cup of Chlorox Bleach each time I fill a tank along with a filter on the hose (Trailer/Camper stores sell them). Last month I opened up all of my three tanks not having looked at them in three years. They were spotless, like new and with no sediment. I also learned a trick from other cruisers here in Mexico who flush their tanks with Cascade dishwashing liquid after putting their boats back in the water. Apparently this cleans out any scum. I did try this in October when I put Hilbre back in the water at San Carlos so I am not sure if my spotless tanks are the result of doing this or using the bleach. Anyway, I was a real happy camper when I peered into the tanks.
John Meyer
Just arrived in La Paz from Mazatlan

I put a couple tablespoons of backing soda in the each tank when I fill them. I have a 'whole house' filter from Home Depot on the pressure side of the water pump, and a drinking water filter on a second spigot at the galley. I occasionally get a bit of taste if the boat sits for weeks (like in the hot summer), and then I'll add just a couple tablespoons of bleach to the tanks, which seems to get rid of it, without making the shower smell like a landromat. This has worked well for us for many years.

This includes Peggie Hall's suggestions:

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