iphone 3gs water damage

Hi all can someone help me please around 2 weeks ago i accidently dropped my iphone down the toilet i quickely took it out dried it off and left it in a bag of rice for a couple of days and it started working normally again.
Since then my backlightkeeps going off sometimes for a couple hours at a time but sometimes a couple days really annoying me now,i have googled this problem and people say take the phone apart and clean inside with soft toothbrush and alcohol but i am not to sure how so i was wanting to know is there a good step by step idiots guide on how to do this or a easy fix for backlight problem.
Should also mention backlight seems to go off when i bump my phone or put it down to hard.
Hope someone can help thanks very much