It is very important that you wash your coffee maker pot and filter container thoroughly at least once a week.
Bitter oils stick to the glass container and plastic filter holder.
I used to wash the plastic filter container and rinse the glass pot. Coffee started to taste bad. When I was told to wash both thoroughly with plenty of soap the flavor improved instantly. Another trick is every time you use your coffeepot, unless you are making another pot right away, put a couple of drops of liquid dishwashing detergent in the pot and run hot water into the pot. Let this sit on the counter till you need it again, rinse and you are ready to go.