I have/had white grout....it will NEVER be as white as original......and I do not have a dog yet.......just boys that dribble round the toilet while learning to aim....LOL...... I think nothing will clean it....just maybe cover it up.......
You may have to chip out the old and put in new grout.......I will never again have white grout......by choice. I sealed with the best sealer too....:
