Cleanliness is one of the four pillars of spiritual life (the other three are mercy, austerity and truthfulness)
The best way of purifying oneself is the pure chanting of Hare Krishna.
Srila Prabhupada commented on this topic as follows:
1) (Lecture 1976). "If we don't lead a brahminical life, we are not allowed to call ourselves brahmanas. You may be the son of a respected high court judge, but if you don't have the required qualification, you cannot call yourself a judge...there has to be an institution for training and educating brahmanas. Everyone should be classified according to his education and his qualities."
2) "Sri vigraharadhana-nitya-nana-sringara-tan mandira marjanadau. Marjanadau means cleansing. The spiritual master along with his disciples is always engaged in cleansing the temple of Sri Sri Radha Krishna. If the cleanliness is neglected, it is a sure sign of laziness. If one is lazy, one doesn't keep his environment clean. "First let me sleep." This is the mode of ignorance, tama-guna. We have to overcome raja-guna and tama-guna. Satvam visuddham vasudeva sabditam.
The heart has to be pure if we want to receive Krishna and allow Him to reside there pleasantly."
3) (Letter 1971). "In India it is custom that the kitchen is not even in the same building where the living rooms are because living rooms are contaminated. After cooking all the pots are thrown away. This is not possible in your country. Therefore you have to keep the utmost cleanliness. Krsna does not require opulent offerings. He appreciates the sincere endeavor. A clean kitchen is more important than an opulent offering. If the kitchen is neat and clean, then the offering will be good. If the offering is a so called "opulent offering" but the kitchen is not clean, Krsna will not like it."
4) (1971 to Rishi Kumar): "Krsna consciousness means to have a clean bead bag."
5) In the early days of the movement, Srila Prabhupada instructed the devotees to clean their plates and the cooking pots right after honoring prasadam. When one of the leaders saw that the devotees were not following his order, he asked Srila Prabhupada which method he should use to get the devotees to the point of following. "The order of the spiritual master should be sufficient,"replied Srila Prabhupada.
6) In Dallas and Edinburgh the devotees complained that there were rats in the temple. So they asked Srila Prabhupada, whether they were allowed to kill them. Srila Prabhupada's answer was: "No, you should be killed because you took the vow of cleanliness but did not keep it!"
7) Srila Prabhupada once wrote to one devotee in London: "Each room should be clean as a mirror, otherwise you invite the rats..."
8) Once, when Srila Prabhupada was on a morning walk in Hawaii, he passed by the prasadam room. Seeing him, the devotees were in so much ecstasy, that they dropped everything and ran after Prabhupada. His Divine Grace led everyone on the compound and then returned to the temple room. Soon later, Guru Kripa complained to Prabhupada about the left over prasadam and the unclean prasadam room and also mentioned how he had difficulties to bring the devotees to the point of cleaning. Srila Prabhupada: "If a devotee doesn't clean, he can go home again and live with his mother."
9) "When you are clean, you are in the spiritual world, Vaikuntha. When you are dirty, you are in the material world."
10) SB 4.2.14-15: "Those who do not regularly bathe are supposed to be in association with ghosts and crazy creatures."