Hi,
I'll check the grout once, the walls have dried out.
I used a diamond disc, until it wore out with a couple of foot to do, so I changed to a black disc, not good and obnoxious fumes.
As I didn't really want to wet the dust, because of mess and it would take longer to check if the channel is working. After the suggestion of an air mover #5, today I tried a vaccuum cleaner with the nozzle outside and the air exit aiming at the cutting, with the door open. This was pretty good, and saved a trip to the hire centre.
C.