ὀρυκτέον
From LSJ
ἄνω ποταμῶν ἱερῶν χωροῦσι παγαί → the springs of sacred rivers flow upward, backward to their sources flow the streams of holy rivers
English (LSJ)
(ὀρύσσω) A one must dig, Ph.Bel.91.19, Ruf.Fr.66.
Greek (Liddell-Scott)
ὀρυκτέον: ῥηματ. ἐπίθ. τοῦ ὀρύσσω, δεῖ ὀρύσσειν, μνημονεύεται ἐκ τοῦ Φίλωνος Βελοπ.