Second that on the plastic tees, or better still do away with them altogether....
Take the outlet from the engine valley heater pipe, straight to the vaporiser. Then the return from the vapouriser to the heater inlet, then the heater outlet to the water return pipe on the engine.
Done that on our 3.9 V8 Disco 2, works a treat, heater is fine and have done away with a lot of potential leakage points and clips.
Peter
PS: You'll find a variety of pipe sizes, the heater stubs are different size to the vapouriser and so on.