Matsya Purana 262.14

262.14

pariveṣaṃ tribhāgena nirgamaṃ tatra kārayet.
vistāraṃ tatpramāṇañca mūlecāgre tatordhvataḥ .. 262.13

The three parts of the circumference should be outside and outlet for water should also be made there and at the base, front and top, there should be space equal to that amount and there a good outlet for water should be made, and half of the Phallus should be made thick—13-14