Mix one part vinegar with three parts warm water. Pour it directly into the top opening. Fill it up to the top rim. Let it soak for at least 20 minutes.
Pro tip: Run the vinegar solution through the taps too. Let a few cups flow out from both the hot and cold spigots. This flushes the inner pipes.
While it sits, scrub the nozzle and drip tray. That little plastic grate is a graveyard of dried coffee drips. Glorious, isn’t it?
