In the Hari-bhakti-vilāsa (sixth vilāsa, verse 30) it is stated that the Deity should be bathed in water mixed with yogurt and milk, accompanied by the sounds of conchshells, bells and other instruments and the chanting of the mantra oṁ bhagavate vāsudevāya namaḥ, as well as the chanting of the Brahma-saṁhitā verses beginning cintāmaṇi-prakara-sadmasu kalpa-vṛkṣa-lakṣāvṛteṣu surabhīr abhipālayantam.
After all inauspicious things are driven away by the chanting of the mantra, the Deity’s bathing ceremony is started. First the Deity is massaged with a large quantity of oil, so that His body became very glossy.
After the first bathing, further bathings are conducted with pañca-gavya and then with pañcāmṛta. Then the mahā-snāna is performed with ghee and water, which is brought in one hundred pots.
The ingredients of pañca-gavya are milk, yogurt, ghee (clarified butter), cow urine and cow dung. All these items come from the cow; therefore we can just imagine how important the cow is, since its urine and stool are required for bathing the Deity. The pañcāmṛta consists of five kinds of nectar-yogurt, milk, ghee, honey and sugar. The major portion of this preparation also comes from the cow. To make it more palatable, sugar and honey are added.
After the mahā-snāna is finished, the Deity is again massaged with scented oil and His body made glossy. Then the last bathing ceremony is performed with scented water kept within a conchshell.
In his commentary on this occasion, Śrīla Bhaktisiddhānta Sarasvatī Ṭhākura quotes from the Hari-bhakti-vilāsa. Barley powder, wheat powder, vermilion powder, urad dāl powder and another powder preparation called āvāṭā (made by mixing banana powder and ground rice) are applied to the Deity’s body with a brush made from the hair at the end of a cow’s tail. This produces a nice finish. The oil smeared over the body of the Deity should be scented. To perform the mahā-snāna, at least two and a half mānas (about twenty-four gallons) of water are needed to pour over the body of the Deity.
After the body of the Deity is cleansed, He is dressed very nicely with new garments. Then sandalwood pulp, tulasī garlands and other fragrant flower garlands are placed upon the body of the Deity.
After the bathing ceremony is finished, incense and lamps are burned and all kinds of food is offered before the Deity. These foods included yogurt, milk and as many sweetmeats as are received.
The Deity is first offered many varieties of food, then scented drinking water in new pots, and then water for washing the mouth. Finally pān mixed with a variety of spices is offered.
After the last offering of tāmbūla and pān, bhoga-ārātrika is performed. Finally everyone offers various prayers and then obeisances, falling flat before the Deity in full surrender.
Ref >> Srila Prabhupada Vani.