FJRiders.com

I used part of a bottle of DOT 4 brake fluid last Thursday…and I need to flush the brakes again today - 1 week later. Is it ok to use the same bottle or should I toss it and buy a new bottle. I’m very diligent at keeping the cap on while I’m working..

It's fine.

It's definitely fine. It should not take on any moisture if the bottle is sealed. Wanna be anal, get some of those heavier than air gasses and fill the bottle with it. That said, I date my container when I first open it, and do not buy the large containers..... we get 355ml bottles here, the biggest I'd go.
I did a rough calculation of total fluid volume of an FJR system.... that small bottle is more than enough, but we tend to overdo it and flush like crazy.... I know people who have used a whole quart to flush an FJR....

If I end out with a larger bottle and have half left over, I just make sure it is sealed tight. Might use it a year later. No problem at all if the bottle is well sealed.