Never used FW tank, need to sanitize for use next week, how?

Sanitize as instructed below and use the tank for what it was designed for..having water to use for showers, cleaning, and drinking. I have used mine for some 30 years with no ill effects whatever. Oh, I just read where bottled water sales declined last year since it all started in the 1970's as more people are starting to realize that they are only purchasing tap water in bottle and creating an environmental nightmare with all the plastic bottls. Yea!!!!