Howto configure a transparent web proxy with own squid server

Hi,

I am running a squid server in a vlan with a whitelist. The proxy works if the user enters the proxy manually to their browsers and systems.

Now I would like to use this in transpartent mode.

I found many documentations how to configure this for fortigate 5.6 but I am running 6.0.2. I tried many different configurations but I am was not able to reach the squid in transparent mode.

Can anyone guide me into the right direction what are the neccessary steps to route all internet traffic to my squid server without manually configuring on all clients?

PS: I know that I can force a whitelist directly in fortigate but sadly how hardware is not fast enough, so with activated white list we loose about 70% of the up/down speed.