Holes in silicone tubing

[snail]

I'm trying to make a return port in my cooler for a RIMS and plan on using a section of silicone tubing w/ holes cut in it for an even distribution. I tried with a drill and a small bit but the tubing just closed back up after I took the bit out of the hole I just cut. What's the secret of cutting holes in silicone tubing?

 

[Hex]

Make a punch.

 

[Hex]

Like this:

http://www.google.com/imgres?imgurl...1t:429,r:10,s:38&tx=94&ty=97&biw=1280&bih=839