Sanitize or replace old camper fresh water holding tank?

This is a great thread.:)
I've been RVing for about 20 years, 3 5ers, and on my 3rd MH now. I NEVER sanitized a water system in any of them. Probably should have, but never gave it much thought.

However, yesterday I did start the sanitizing process on the Bounder. I used the sodium-dichlor???????, the stuff I use in my hot tub (it's 99%)vs 3% in household Clorox. I used a tablespoon full for an 86 gallon tank.
I'll flush it really well this evening.