Painting Discolored Grout?
They make grout cleaners. You can pick them up at your local DIY store. Kelvin is right in that you should avoid the acids. There is a brand made in an orange bottle, and it works excellent, spray on, wait 2 minutes, srub off. After that dries you should then...
Urine Stained Grout?
Home depot makes a grout cleaner in a large orange bottle, its amazing. Spray on, wait 2 minutes and wipe clean. Its also excellent at cleaning tiles with texture or divets. After cleaning though, you would want to seal the grout, with a grout sealant to prevent...