In answer to your first question:
Is this method correct for a moulded tee's?
Yes this method is fine.
For your second question:
How should this type of connection be accurately modelled?
the answer is "You can't". Note that
CAESAR utilizes the
3D Beam element. This is essentially an infinitely thin stick - with properties such as diameter, thickness and modulus. The concepts of volume, surfaces, thickness variations and so forth are beyond the capabilities of this element. You are limited to uniform cross sections, and overall system behavior.