Can Wet and Forget be used in a basement?
No. From their FAQ:


  Can I use Wet &amp; Forget indoors?
  
  Wet &amp; Forget is specially formulated for outdoor use and requires
  exposure to the weather to work properly. For indoor use, we recommend
  Wet &amp; Forget Indoor Mold+Mildew Disinfectant Cleaner.


See:  Wet and Forget FAQ