Paul's advice of using an acid rinse is the traditional well proven route to take.
I would, however, advise a dye test for the acid rinse. In recent years there has been quite a few instances of cotton having a pH sensitive dye. My advice is on arrival to do your normal dye tests but also just dab a little neat acid rinse somewhere out of sight, say a zip panel. Leave it while you get on with the vaccing and set up. You should know within 10 minutes or so if there's going to be a colour change to the fabric. If there is, keep EVERYTHING pH neutral, but still test first.
It's rare, but it can happen.
SAFE and happy cleaning
Ken