Quoted: I just picked up two 55 gal water drums.  Do I need to clean them before filling?  What is the best (and easiest) way to treat the water?

Depending on what was in the barrels to begin with determines how to clean them. After cleaning fill with water and add regular Clorox bleach (16 drops to the gal) store in a dark area to reduce the growth of mold. Make sure you have a pump or some way to get the water out. Once they are filled you won't be moving them to easily.

I would rinse them out with a water bleach solution (cap full of bleach to the gal)
Then fill and add bleach as recommended. You should be good to go.

I also have two 55 gallon barrels.
Mine is a slightly different question.

These were bought new and used for water storage.
I had a house built, and during that time, moved into an apartment. Barrels were emptied and left open to air out/dry. Barrels were placed in storage (open ) for 6 months.
When house was finished, barrels were eventually moved to house.

Barrels have been empty and open now for more than 4 years, in an outbuilding. I wish to wash them out, and refill them. I know I've got dirt and bugs/spiders/webs inside.

Question is:

Should I just powerwash them as well as I can, and run a bleach solution through them?

I was using this stuff, and I have some left, but it's over 8 years old. Think it'll still be ok to use?

Since they'll be exposed to freezing weather, only fill 4/5 or so?

Thanks.


HKO

Dirt, bugs, webs aren't that bad.

I've never heard of that stuff.  Just use the tried and true bleach.