IME it’s the softeners that cause those lovely aromas of some washing machines.
My washing machine still smells the same as the day it was delivered. I use that Dr. Otecker shit that someone else mentioned, about once every two months. I never use softener but I do use the liquid detergent (Sainsbury’s own brand). Nothing goes in the draw so the ribbed pipe isn’t exposed to anything but water. I dry the tray and the door seal and all its folds thoroughly every wash and leave the door open to air.
Again; it smells like new 3 years down the line, washing eveyday clothing as well as biking loads.
Softener doesn’t make any difference to the ‘softness’ of your clothes, it simply makes them anti-static.
Just my two-penneth.
Edit – And once you’ve used the stuff, that’s it. It just sits in the tank, collecting all of that dirt and muck. Festering. Growing. Becoming self-aware…