Muriatic acid is hydrochloric acid... or HCl if you prefer. Pure HCl is a gas. The gas is "dissolved" in water to make a water solution of about 30% HCl in the water. This is generally referred to as concentrated hydrochloric acid (or muriatic acid if you buy it from the hareware store). It will be 95-99% pure, but still be only about 30% acid. Sound confusing? it is.
Start dilute and go stronger. I cleaned a bunch of stuff in a 2:1 mix of water to muriatic acid. That was probably stronger than I should have, but chemicals don't scare me. I only left it in there for about 5 minutes. Lots of bubbles! Do it outside and keep the fumes out of your eyes and nose. Rinse it off immediately after wards with lots of water. My pieces were small and I wiped them down then baked them in the oven for 30 minutes at 250 to remove any remaining water.
For disposal. Assuming your using the more dilute solution that you mention. Go to the store and buy a new box of Arm and Hammer baking soda. Bring it home to your wife and tell her that you are going to change out the old box in the freezer with this new box. Tell her you love her and you love her cooking and you just wanted to help her out. Don't tell her that you are going to take the old box and dump it in the dilute muriatic acid solution. There is no advantage to the old box in the freezer, but why not use it for your essentially disposal needs instead of the new box? Plus it'll keep you in good with the wife, so you can keep feeding your old truck habit.
The baking soda (sodium bicarbonate) is a weak base that will neutralize the strong acid. Dilute with lots of water and dump it down a drain or in a ditch.
