I want to know how can one sterilize their intestine (both small/large) and what are the consequences.
It isn't possible to completely sterilize the gut of a living person. Repeat: not possible under any circumstance in a living person.
You can dramatically decrease the number of organisms by using high-dose antibiotics and flushing out the gut copiously, and by copiously, I mean your intake plus an osmotic agent is so high that you have explosive diarrhea that looks like pure water. (It's not.)
Even with all this, swabbing will reveal plenty of CFU's (colony forming units) from what appears to be a perfectly pristine gut.
Drinking several gallons of household bleach would give you even less desirable results, not to mention it would kill you.
That's not to say there aren't any animals with perfectly microbe-free intestines. There are germ-free mice, rats, and possibly a few other animals by now. Obtaining them is difficult: they must be harvested by sacrificing a pregnant female, and under the most stringent sterile conditions, removing fetuses from the uterus, and growing the offspring in a sterile environment, feeding them sterile food (obviously processed), etc. Allow these animals to reproduce, and the result is- eventually- germ-free colonies.
The cost is phenomenal. If it were possible to sterilize mice guts more easily, it would have been done.
Note: the following answer has been completely rewritten.
There are a large number of microbes in the intestines, their presence is essential for being able to digest food properly. The lining of the intestines contains living cells, so any method that completely sterilizes the gut will also do severe damage to the gut. Sterilizing the skin, in contrast, is a different matter, in that case far UV-C light can kill microbes without doing damage because far UV-C light doesn't penetrate the skin deep enough to affect living cells.
This means that the only safe way to do this (involving aggressive chemicals, radiation or whatever other means) is to make sure the patient will survive with damaged intestines, and that requires putting the patient on total parenteral nutrition.