Hey Martin, I looked into this, My filter inserters, splitters and combinators have no problem picking "Dirty Barrel" as a filter in 0.17 and 0.18.
Perhaps it's down to localization, check under "Unsorted" and see if it's there if you're playing 0.17.
In know in the German locale it's called "verschmutztes Fass"
Under 0.18 it's correctly listed under "Intermediate Products".