The headword is the third person plural, imperfect indicative active, of the verb fu/rw 'I mix'. Compare, with similar glosses, phi 852 (third person singular, present indicative active, of the same verb).
Similar entry already in Hesychius epsilon7556, who adds the gloss e)mo/lunon ('they were staining').
The headword is quoted from Homer, Iliad 24.162, where Priam’s sons were 'mixing' their garments with tears (web address 1). This would explain the associations with washing and inundating. Furthermore, the gloss of this Homeric line in the D scholia is 'they were drenching, they were inundating'.