Looks like that in my machine

There is a brush that came with it and the manual said the same, but after 5 years of family use, that stuff was not only in the front anymore. I had to use a pressure washer and some chlorine based detergent to get rid of everything (if I knew about an ozone generator back then I might've tried that against the odor).

YMMV. If you're using it e.g. in a 2-person household you might never have that issue during the whole expected lifetime, but with our usage and especially all that babystuff, that happened, and I hated it 😅.