I am getting ready to put mauranic acid on my basement walls to etch them before sealing them. What is the best way to apply the acid?:)

Tell us more about what you are doing. Never heard of a need to etch basement walls before.

Holy smokes man, be careful!

I use muriatic acid for concrete etching on concrete storage tanks, before coating them with epoxy liners. So, I am very familiar with it.

It can kill you, burn your skin, burn your lungs, burn your eyes... that is just the fumes, not the actual contact. Upon contact with the surface, the fumes will instantly take your breath, and make you start coughing. You can't catch your breath until getting away from them. I assure you, I am not exaggerating.

Are you working inside the basement, or are you working on the outside wall? If you are inside, you better seal everything in the rest of your house from fumes.

Remember, it is also extremely corrosive. So, it can quickly corrode metal pipes, your furnace, exposed metal ductwork, etc. If you have any windows, open them, and put a fan outside of them to pull the fumes out.

For the procedure...
1-Start by putting on tyvek coveralls. They're inexpensive, and can be found in safety gear sections of building supplies.
2- Put on your respirator with organics cartridges, or you might be able to get a disposable carbon-based mask
3- Put in 1/4 muriatic acid, and 3/4 water in a pump/ garden sprayer. It will trash the sprayer one time through if you don't use viton seals in your sprayer. But, for the difference in cost, you should probably just by the cheap one and throw it out when you're done.
4- since you won't have a full face cover, wrap some damp towels all over your face and neck.
5- put on safety goggles
6- spray it on the wall , and work your way from the bottom-up doing 6' or so sections at a time.
7- after setting for about an hour, rinse thoroughly with clean water
8- if it is inside, and you have a sump pump that will be carrying out the water, make sure you run lots of water through the pump, or it will be toast
9- after thorough rinsing of everything, including sprayer, mix 25% ammonia, 75% water in your sprayer- safety gear back on especially respirator! Ammonia fumes are very strong!
10- spray everything down with ammonia solution, let it set for 30 minutes
11- rinse everything down thoroughly with water

You'll need to let them dry for probably a whole day before applying your sealer. Unless your sealer says that it can be put on damp surfaces. Some fans will probably help the drying process.

Be very careful. Please!
Al

Okay, so I have decided to skip the wall etching step of sealing my inside basement walls. They have already been painted by the previous owner and I am afraid that the wall sealer paint (Leaktight I think it is called) will not adhear as well. Anyone ever painted over a previous sealer? How did it work?

Try a test spot and see how it works, should be OK unless the old paint is loose and flaking off the wall. Glad your not going to use acid on the walls.

I don't have any experience with basements, so I can only tell you from sealing concrete tanks, etc. I always have to seal on the side that the water is pressing against. In this case the water is pressing against the outside wall. I know I have seen other posts on this site about how to seal on the outside wall.

I personally think you will have a very difficult time getting it to seal from the inside. But, if I was going to try it... I would wire brush every inch to knock off loose paint. I would clean with bleach and water mix to kill any mold, mildew. I would pressure wash. Let it dry a day or 2. Then, apply the sealer. I personally would use 2-part epoxy paint since I know it is effective.

I know that sounds over-kill. But, prep work is the most important part of painting. If you stand any chance of sealing the moisture out, your prep work is critical.
Al

You are right, sealing from the outside is the best approach. And the prep-work you are describing does not sound like overkill to me.