How to add new PF rules everytime InternetSharing is started?

I am using InternetSharing and running a web proxy to redirect all traffic through.

How may I automatically add the correct redirect rules to the anchor InternetSharing is :
Code Block
com.apple.internet-sharing/base_v4


Where is the documentation to manage anchors in a constructive way not interfering with the GUI "System Preferences..."?

How to add new PF rules everytime InternetSharing is started?
 
 
Q