Matsya Purana — Prologue to the Matsya Purana and the Manu–Pralaya Rescue Narrative
ततः स मनुना क्षिप्तो गङ्गायामप्यवर्धत यदा तदा समुद्रे तं प्राक्षिपन्मेदिनीपतिः //
tataḥ sa manunā kṣipto gaṅgāyāmapyavardhata yadā tadā samudre taṃ prākṣipanmedinīpatiḥ //
Then, when Manu cast it into the Gaṅgā, it continued to grow there as well; and so, time after time, the lord of the earth (Manu) threw it into the ocean.
It foreshadows the pralaya narrative by emphasizing the miraculous, unstoppable growth of Matsya, prompting Manu to move it from river to ocean—an omen of a cosmic-scale event.
Manu is called “lord of the earth,” portraying the ideal ruler/householder as attentive and responsible: when a situation outgrows a smaller setting, he acts pragmatically for safety and order.
No direct Vāstu or ritual procedure is stated; indirectly, it reflects the principle of choosing an appropriate “container/space” for what is being protected—moving from a small water-body to a larger one as necessity demands.