If you own a white wax candle then you're fast on your way to having gleaming grouting between your bathroom tiles.
Or so this video from Rumble suggests.
Simply rub your candle along the grouting so that there's a generous layer of wax.
This will then offer a layer of protection to the lining of your tiles so that when water splashes on it, it won't mould or discolour.
Snazzy, huh?