Radak: Chaser does not refer to Tzapachas, rather, to ha'Shemen, which is masculine. Above (verse 14) it says "Lo Sechsar", for it refers to the flask. Both mean the same. Usually when there is a compound noun, the verb is conjugated based on the first word, but sometimes it is based on the latter, e.g. "Haysah Elav Pnei ha'Milchamah" (Shmuel II, 10:9), "Kol Negidim Nechba'u" (Iyov 29:10). "Keshes Giborim Chatim" (Shmuel I, 2:4).