Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
stercŏrārĭus, a, um, adj. [stercus], of or belonging to dung: crates, Varr. R. R. 1, 22, 3: porta, a gate in the temple of Vesta (v. stercus), Fest. p. 344 Müll.; cf. Bunsen’s Rome, 3, p. 12.