Wallace understands you have to rock that brush as you use it. (Thats why the pile-wotsit surface is curved  - moreso, if you ever saw it, the Realistic version of the brush.)
You spread your cleaning solution/scrub  using one  end of the pile, then you tilt back and remove it with the dry (unused) end.
Wallace has reservations about this method of cleaning.
Seems that -without suction - your just merely rearranging/shifting residue/grit/mold.