Religion: how can I turn my gay nephew straight ?

You can't.  We have no direct control over what attracts or tempts us.  His temptations might always be with him.  There is no sin in this, only in what we do about them.  Encourage him to follow Christ rather than his own lusts.  In any case, be loving and welcoming even if you can't permit gay sex in your house.

Show him that it's a filthy thing,it causes diseases

Your opinion is ridiculous ignorant horseshit.

You probably can't.  Your opinion is just that - an opinion, and is not based on fact.

Here’s an idea...MIND YOUR OWN BUSINESS!

I've seen animals that were gay.

Do you think he could turn you gay? If not, why do you think you, or anyone else, could possibly turn him straight? He was born that way. Homosexuality is a normal part of human sexuality and it is not limited to humans. It has been observed in over a thousand different species including all the primates. All studies have shown that it is beneficial to the survival of the species which is why it has not been selected against by evolution.  Looking at girls means nothing as far as his sexuality is concerned.

Simple answer - you can't.

There is nothing you can say or do that will change how he feels or how he wants to live his life.

BTW - using animals as an example is not really proof of anything.  I had a pair of MALE rabbits that would constantly try to hump each other anytime they were in the same cage.  And a male dog will hump ANYTHING that holds still long enough - including your leg or anything else that is convenient.

So - try again.  

Well your thinking is faulty.

Sexuality is not black and white and to think it is appears to be very childish.

Your lack of ability to accept reality is the real problem.

How would you feel if he said

"how can I turn my straight niece gay ?

 I do love her but it kinda disgusts me to see her flirting with men. "

In his opinion he believes straight people are choosing to be straight.

Understand?

Untwist your nuts, hon.