You don't have to submerge the rock in vinegar. Actually, vinegar is a poor test because it is a weak acid.
There are a couple of things to keep in mind when thinking about adding rocks to the aquarium.
One is whether the rock contains any heavy metals. This is difficult to test for, so if you know what type of rock it is, that helps.
The second is the more common issue, which is adding a rock that contains a high level of carbonates. Carbonates dissolving into the water will make the water harder, and can cause issues over time (depending on the concentration of carbonates).
There are two different reliable tests for carbonates that you can do at home:
1. R/O leech test
2. Acid test
The R/O test is easy. Dump some R/O water into a clean bucket, and run an airstone in it for an hour or so. Test the pH of the water and record it. Drop the rock in. In a week, test the pH again. If it has changed, the rock is altering the water and shouldn't be used.
The acid test is easy as well, depending on what you have on hand. Vinegar that we generally keep in the kitchen can be used in a pinch, but it's a weak acid. Dribble some of it onto a clean, dry rock. If it fizzes, the rock is unsafe. A stronger acid is better, like hydrochloric acid (also called muriatic acid). If you want to, you can pick up muriatic acid in the solvents section at Home Depot. However, if you have an API water test kit like most of us do, the Nitrate #1 bottle contains hydrochloric acid. Squeeze a couple of drops onto the rock, and watch for fizzing. If it fizzes, don't use it. If it doesn't, you can wash it off again and use it.
If you need to sterilize a rock (and I recommend you do), soak it in a bleach solution for a while, and then rinse with clean water, then soak in regular water tht has been treated with a double dose of water conditioner. Then rinse it again, and soak again with the conditioner before adding it to the tank. Never, ever boil rocks!
I blame spelling mistakes on my iPad. You should too!