when posed by deep philosophical questions like this, I find it best to consult the only book man needs to read: The Bible
1 Corinthians 7:3
The husband should give to his wife her conjugal rights, and likewise the wife to her husband. For the wife does not have authority over her own body, but the husband does. Likewise the husband does not have authority over his own body, but the wife does. Do not deprive one another, except perhaps by agreement for a limited time, that you may devote yourselves to prayer; but then come together again, so that Satan may not tempt you because of your lack of self-control.
Leviticus 18:22
You shall not lie with a male as with a woman; it is an abomination.
Now you may say that trannies are allowed because they are men in womens clothing and therefore treated as women. Alas, no
Deuteronomy 22:5:
A woman must not wear men's clothing, nor a man wear women's clothing, for the Lord your God detests anyone who does this.
From all that it is clear that it is gay and a sin to do anything but insert a penis into a vagina and have unprotected sex. That includes oral sex, anal, masturbation, docking, scat, golden showers, fisting, prostate massage, and jelqing.