DIAGNOSIS Old coffee oils and mineral deposits from water are baked onto the aluminum, which absolutely ruins the flavor. A simple rinse isn't enough.
FIX Do a deep clean monthly. 1) Let the pot cool completely. 2) Disassemble it fully: top chamber, filter basket, gasket, lower chamber. 3) For the aluminum chambers, use only warm water, a soft brush (an old toothbrush works), and a tiny bit of mild dish soap. Rinse thoroughly. 4) For the filter basket and the tiny holes, use a stiff-bristle brush (like a bottle brush) and hot water. Never use steel wool or abrasive pads on the aluminum. 5) Wipe everything dry before reassembling.
IF THAT DIDN'T WORK For stubborn, baked-on residue or a persistent bitter taste, you need to descale. Fill the lower chamber halfway with a 50/50 mix of white vinegar and water. Assemble the pot without coffee and run it through a cycle, letting the vinegar solution steam through. Then run 2-3 cycles with just clean water to rinse.
HEADS UP Never put any part of this in the dishwasher. The detergent is too harsh for the aluminum and will cause pitting and a metallic taste. Hand wash only.