The proper way is to see if your work has proper chemical disposal instructions. In the case your work does not, you should be able to dump NaNO2 down the drain when it has been dissolved with water. As long as you're not dumping it in a drinking water supply, you should be okay. An explanation for this is because once it has been oxidized and dissolved with water, it'll turn into nitrate and that's already something that exists in our ecosystem.
How much you are dumping is what matters. If you have tons of it, I would not recommend disposing it down the drain. Instead I'd look at properly disposing it. If it's a couple grams you'll be okay.
