According to Scripture, the purpose of a male/female marriage is to be fruitful and multiply. Obviously, the male has a part that fits the females part by God's design. Now, does every time the act of sex produce a child, no, but I guess where the thought of practice makes perfect comes into mind. But one thing is for certain, oral sex and anal sex cannot ever produce children. That leads to the thought process that those sexual acts are not what God had intended (and why Homosexuality is a sin because any acts by same sex partners can never produce children).
As far as masturbation is concerned, will it be fruitful and multiply?
If we stay within the confines of what God instructed Adam and Eve, we can easily deduct what God's intent was compared to what our lusts contradicts.