Some drip coffee makers require periodic cleansing with a solution of water and vinegar.If you have a coffee/teapot, the inside of which is stained with oily
brown residues - also plastic/metal coffee filters, tea strainers, and stainless steel sinks in caffeine-o-phile houses - they can be restored to a shining, brand-spanking-new state by washing in hot washing powder (detergent).
Get a large plastic jug, add 2..3 heaped tablespoons of Daz Automatic or Bold or whatever, and about a pint of hot water - just off the boil is the best.
Swill the jug around until the detergent is dissolved, and then pour
into tea/coffeepot, and let it stand for 5 minutes, swilling the pot around occasionally, just to keep the detergent moving. Put the lid on and shake it a few times (care: slippery + hot)
Repeat as necessary. Keep it hot with a
little boiling water if needed. If you have a cafetiere, dissemble it, and soak the parts in the mixture for a few minutes, agitating occasionally.
In both cases, the residue just falls off with almost no scrubbing. It does great
things with over-used filter machine filters, too.