Dharma sastra-Ānhika prakaṇam-Gaṇḍūṣa
The word Gaṇḍūṣa means rinsing mouth. As a part of cleansing process, dharma śāstra had prescribed to perform Gaṇḍūṣa with water. Mainly after passing urine, excretion and completion of meals, Gaṇḍūṣa is said to be performed. There is also specific number of times that the rinsing is to be done.
Apāṃ dvādaśa gaṇḍūṣān purīṣotsarjane budhaḥ | mūtre tu caturaḥ kuryāt bhōjanānte tu ṣoḍaṣa ||[1]
It means that one should rinse their mouth 12 times after exertion, 04 times after passing urine, 16 times after completing meals. It is prescribed that the rinsing of mouth should be done while sitting, i.e. one should not rinse mouth while standing. After rinsing one should spit the water on their left side. Because it is believed that the devatās reside on the right side of vipras.
Viprasya dakṣiṇe bhāge devatāstiṣṭhanti nityaśaḥ | āsīna eva gaṇḍūṣān vāmabhāge visarjayet ||[2]