Pull the tank out, open it up and dump the old ink and media. You can actually rinse the ink out of the media, dry it and put it back in (takes forever to dry, fyi) or you can fill with some absorbent material. Use your chip resetter to reset it and put it back in.
These tanks do not actually do anything but catch waste ink. They don't weigh it and let you know when it's full or anything like that, epson has a counter system that sounds the alarm after x prints on the machine or whatever. And there's no need whatsoever to purchase a new one when this happens so long as you clean or replace the media, it's just a wasteful trick to get you to by more OEM stuff from them.