‘The male servants of some men carry on the mouth congress with their masters. It is also practised by some citizens, who know each other well, among themselves.” The Kama Sutra of Vatsyayana 
Some women of the harem, when they are amorous, do the acts of the mouth on the yonis of one another, and some men do the same thing with women. The way of doing this (i.e. of kissing the yoni) should be known from kissing the mouth. When a man and woman lie down in an inverted order, i.e. with the head of the one towards the feet of the other and carry on this congress, it is called the “congress of a crow”.’ For the sake of such things courtesans abandon men possessed of good qualities, liberal and clever, and become attached to low persons, such as slaves and elephant drivers. The Auparishtaka, or mouth congress, should never be done by a learned Brahman, by a minister that carries on the business of a state, or by a man of good reputation, because though the practice is allowed by the Shastras, there is no reason why it should be carried on, and need only be practised in particular cases. As for instance, the taste, and the strength, and the digestive qualities of the flesh of dogs are mentioned in works on medicine, but it does not therefore follow that it should be eaten by the wise. In the same way there are some men, some places and some times, with respect to which these practices can be made use of. A man should therefore pay regard to the place, to the time, and to the practice which is to be carried out, as also as to whether it is agreeable to his nature and to himself, and then he may or may not practise these things according to circumstances. But after all, these things being done secretly, and the mind of the man being fickle, how can it be known what any person will do at any particular time and for any particular purpose.
THERE are two kinds of eunuchs(homosexuals), those that are disguised as males, and those that are disguised as females. Eunuchs disguised as females imitate their dress, speech, gestures, tenderness, timidity, simplicity, softness and bashfulness. The acts that are done on the jaghana or middle parts of women, are done in the mouths of these eunuchs, and this is called Auparishtaka. 1 These eunuchs derive their imaginable pleasure, and their livelihood from this kind of congress, and they lead the life of courtesans. So much concerning eunuchs disguised as males. Eunuchs disguised as males keep their desires secret, and when they wish to do anything they lead the life of shampooers. Under the pretence of shampooing, a eunuch of this kind embraces and draws towards himself the thighs of the man whom he is shampooing, and after this he touches the joints of his thighs and his jaghana, or central portions of his body. Then, if he finds the lingam of the man erect, he presses it with his hands and chaffs him for getting into that state. If after this, and after knowing his intention, the man does not tell the eunuch to proceed, then the latter does it of his own accord and begins the congress. If however he is ordered by the man to do it, then he disputes with him, and only consents at last with difficulty.
From – The Kama Sutra of Vatsyayana, tr. by Richard Burton,