Hello BurtSt
We recommend filling the Braava jet m6 tank with normal water or adding some of the iRobot detergent to the water in the tank if needed. You can find this here for example:
iRobot Hard Floor Cleaning Solution (1 -part)
We hope we could help you with this.
Best regards,
Your iRobot Team

No, only water, no detergents are needed as cleaning is done with special cloths.