Cleaning water storage tanks

[Gavinsredseareefer]

Hi. I have 2 65 gallon storage containers I haven’t used in a while. Anyone have any insight or tips on how I can clean them to start storing water. Thanks!

[DarStar301]

I just cleaned my 55 gallon storage tank full of build up from mixing salt. Bought some citric acid powder from Amazon, let it sit over night. I then gave it a good cleaning with a power washer.