Adam Funk wrote:

I've been working on tidying up the grout in the shower by applying
thick bleach with a paintbrush, leaving it for a while, then rinsing
it off. I'm wondering --- would it be more effective if I made it
even thicker so it stayed in place better, & what is a good way to do
that?

Baking soda? It seems to be latest "New! Improved!" ingredient in
bleach the shops, maybe you could add enough to make a paste?