The Compendium of Caraka 4.8.10

4.8.10

tata ṛtvik prāguttarasyāṃ diśyagārasya prāgpravaṇamudakpravaṇaṃ vā pradeśamabhisamīkṣya, gomayodakābhyāṃ sthaṇḍilamupalipya, prokṣya codakena, vedīmasmin sthāpayet/

Then the officiating priest, examining a site sloping to the east or sloping to the north in the north-eastern direction of the house, smearing the sacrificial mound with cow dung and water, and sprinkling it with water, should set up the altar upon it.