αὐτὸν κέκρουκας τὸν βατῆρα τοῦ λόγου → you have struck the very threshold of the argument, you have struck the most important and chiefmost point
P. ὑδροπότης, ὁ (Xen.).
be a water-drinker, v.: P. ὑδροποτεῖν (Plato).