I dye my hair with bright, off-the-wall colours very often. The worst part of it used to be spending an hour or two cleaning up the bathtub with harsh chemicals and abrasives, trying to remove all the deeply embedded dye. Now I use (literally) a drop of super cheap oil that I get from the 99 cent store and rub it into the cracks and crevices in the bathtub as a preventative measure. I dye my hair, wash it, and none of the colours sink into the cracks. When I'm done, I just wipe the oil away then clean the bathtub as usual. I wish my poor mum did this for all the years I was dyeing my hair as a teen!
This is such a great tip! I have dyed clothing in my bathtub in the past and it was blue for many months. It would probably be good for keeping paint splatters from sticking as well. I don't have a utility sink so I use my tub for all sorts of projects.
I do the same, too. Tub projects! I think of it like when you put vaseline on your hairline to keep hair dye out of your facial pores. It's so ugly when it sinks in and hurts to remove! This works the same. :)