Gd2shoe asked for me to chime in on this discussion (having some long-past experience with Shorewall), so I looked up some documentation that might be helpful to you. It's been several years since I've used Shorewall, so I don't know how much help I will be, but here is something you might find useful:
http://www.shorewall.net/Shorewall_Squid_Usage.html
Also, there is a lot of documentation for Shorewall on their site. Here's the index:
http://www.shorewall.net/Documentation_Index.html
It's important to know what version of Shorewall you're using, as its usage has changed drastically over the years. Which one is it?
You may also need to add some "related" or "established" rules in, but I don't remember how to do it off the top of my head, and the syntax has probably changed since I last did it. The above pages will hopefully be helpful to you.
--Dane
