I'm going to second mikes advice about wearing rubber gloves and safety glasses, especially if you can't guarantee that the container is properly sealed. If you get any on you, simply flush with lots of water, and apply a paste of baking soda and water to neutralize (I would flush first while someone else mixes the paste). For transport, just make sure that you have something that will keep it from tipping over.
OK, now to the reason I answered: places that you can take it.
The easiest is if your town or city sponsors a hazardous waste day or provides a hazardous waste dropoff (more likely in a large city). Call first to ensure that they take acids. Most will, especially acids that are commonly used in home improvement, such as sulfuric and hydrochloric (aka muriatic).
If you have a relationship with a repair shop, you can call and see if they'll take it (for use with batteries). They probably won't, and a stranger definitely won't, but it's worth asking.
A metal plating shop is another possibility. They probably won't accept it for use, but might dump it into their waste drum for a nominal charge.
Finally, if mikes scared you, there's Clean Harbors or similar companies. They'll come to your house and scare you even more, and you'll pay through the nose. But it will be gone.
Yes. I used to keep my acid in a large container along with some paint thinners and removers. Even with the acid bottle tightly sealed, the metal paint thinner containers rusted after a couple of weeks. Will enough vapors get at your ducts to rust them? Can't say, but it's worth the effort to wrap them. Sounds like your major problems will be containing the acid so it doesn't reach the floor and neutralizing it without flooding the inside.
Best Answer
HCl can be combined with baking soda to form salt water and CO2.
NaHCO3 + HCl = NaCl + H2O + CO2
NOTE this is exothermic and effervescent, mix slowly, adding the soda to the acid. In a wide-mouth container.