Send it back to your respective manufacturer is one of the most and common way to properly dispose printer-post-consumer wastes. Notice that whenever you purchase replacement cartridges from branded manufacturers, they often include a special envelope inside the packaging. This indicates that the product can be returned once empty or used, and the envelopes you kept will make use by then. Mailing the cartridges back to the manufacturer requires either a box or a seal pack where you'll put the items. Additionally, most big names in the print industry such as Hewlett-Packard, Epson and Dell, these companies are willing to provide 5-10% rebates to all customers who will participate in their recycling programs. No one should worry about the shipping or mailing costs, as they will shoulder the expenses for you.
A non-profit organization that gladly accepts used printer cartridges as donations is one of the perfect choices you have. Globally, there are a few of these organizations that you should be familiar with if your planning to support such one. Local groups are also a good choice, they receive cash or monetary donations from different manufacturers for every recycled toner cartridges and ink cartridges they provide.
If charitable works are none of your business, and you certainly need cash in exchange of your empty cartridges, then might as well sell it directly. Since there are non-profit organizations, of course they have a counterpart. Consider it their business, accepting certain amounts of used cartridges from people who are in need of cash. These option, unlike the drop box recycling programs of many branded manufacturers, you can't just give them three or four cartridges. Perhaps 10 items maybe good enough, but that's the least, a box of used ink or toner cartridges is more likely sufficient. With this option, you have to wait much longer to gather enough until you reached at least their minimum requirement.
Now if you're not concern of any money, and that you just really want to get rid of your post-consumer waste, then how about you give a visit to any Office Depot or Staples branches near you. These two stores are now accepting used ink and toner tanks for your convenience. Since they'll be taking your own garbage, neither of you will give or receive any money. Just simply take the items with you, visit their store and find the bins marked with cartridge recycling logos. If you can't find any, look for a personnel or go straight to their customer service to ask for help.
If you want a bigger role to help the environment, you may consider setting up your own recycling program in your neighborhood. It isn't hard to spread the news around that you're accepting used and empty printer cartridges, then place a recycling bin just around an accessible corner where anyone get drop their items. This sounds absurd, but come to think of it, once the bin is full of plastic ink and toner tanks, you can sell it in exchange for cash. Wouldn't that be nice, helping your neighborhood get rid of their junks, while you're getting some small amount from gathering their waste?