Hi all would appreciate some advice on how/when you clean your grey grout off black tiles. when I have started cleaning off grout in the past and present job the residue takes some getting off the tile. I leave the grout for the required setting time before cleaning off a few times. Is it best to then wait for the grout to fully set then clean remainder the following day ? how do you all approach this problem. I have tried both sponge and washboys. thanks in advance