@Frank342 I've used muriatic acid for lots of things. If you are using it to clean grout, mix it half and half with water. Then scrub with a brush. I've never had to use a mask, because I've only used it for small jobs and don't have my face right down there like you would scrubbing grout (But you definitely need gloves and eye protection as well). However, be aware that muriatic acid will dissolve cement products if left on too long. So you'd just use it to scrub the grout, then immediately wash it off with plain water, doing small sections at a time.
It also works great for cleaning stained toilets and toilets that aren't flushing well. If your toilet doesn't flush strongly, the little holes just under the rim are often plugged up if you have hard water. What you do is shut off the water valve to the toilet, flush the toilet so almost all the water in the tank is gone. There shouldn't be any water in the tank above wherethe flapper sits- if there is, soak it up with a sponge. Lift the flapper and pour a cup of muriatic acid in. Leave it overnight, or at least 4 hours or so (put something on the toilet lid to remind yourself not to use it). In the morning you'll see a lot of dissolved gunk in the bowl. Turn the water back on, let the tank fill, then flush. Usually need to scrub a bit right under the rim where the holes are as well, but after the o'nite acid treatment, it scrubs up easily.
Vinegar may also work for this, I've never tried.
And, by the way, I am on a private septic and the muriatic acid does not seem to do anything bad to it- have never had to have it pumped in the 11 years since it was new. But I do try not to use the acid more than once every few months.
