If internal overflow, What type of standpipe do you have now?
Some people use sponges, filter floss, endcaps on top of thier standpipes can be altered as in the so called "Durso standpipe"
Describe your overflow situation
Thomas
Here is what I did and it worked awesome. I am 15 and had no problems making this contraption. I am going to say it again the thing is almost silent now.
Here these websites ill help you: First Link Second Link
You won't regret it.