The affix ṇamul comes after the verb piṣ 'to grind' when a word in the Instrumental -3rd case denoting 'liquid' is in composition.,
Thus उदपेषं पिनष्टि = उदकेन पिनष्ठि (VI. 3. 58.) 'he grinds with water'; तैलपेषं पिनष्टि 'he grinds with oil'. Here also 3.4.46 applies, and an appropriate verb from the same root is employed to govern the gerund.,