am curious as to what people are going to put here as my bathroom tile grout looked a bit dingy so I got one of those pens, biggest load of rubbish ever. more dripped down my sleeve than went on the walls
I just spray some bleach solution (1/3 bleach, 2/3 water, mixed in one of those plant spray bottles) onto mine, then rinse off after an hour... lovely white grout again ! If the grout is really badly stained, I find scrubbing it gently with an old toothbrush removes the discolouration.
I can recommend this stuff http://www.wilkinsonplus.com/invt/0160039
It was hassle free and brought the grout up like new. You could find it in other places other than wilko, its just that I bought it from them. wouldn't recommend using a bleach solution as it will eat through the grout eventually.
i've been using a bleach solution for years, and sometimes neat bleach and an old toothbrush, and it's not eaten through any grout yet. certainly keeps it looking sparkling white though.