The object of the verb kṛ takes the 6th-Case-affix, when it means 'to impart a new quality or virtue' -- gandhanāvakṣepaṇasevanasāhasikyapratiyatnaprakathanopayogeṣu kṛñaḥ [[1.3.32]].,
Ex. एधोदकस्योपस्कुरुते 'the wood gives a new quality to the water' (or he prepares the wood and water for sacrifice). (By 6.1.139, स is inserted).
When प्रतियत्न is not meant, the second case-affix is employed: as कटं करोति.
The word शेष is also understood here. So that we have also एधोदकमुपस्कुरुते ॥,