Cheers for the pic Brett and suggestions everyone.

The problem is that I'm running 4" and all the other bits are 3".

Yes mate, thats what I'm thinking I might have to do, leave the square connection and find a 3" to 4" reducer to put on and hose clamp it.

I just don't trust that poxy little 75mm x75mm square connection that is already on there. I'll fix that as well whilst I'm doing it.