Struggling to constrain pipe fittings in an assembly

[Stu3d]

I have an elbow and tee which just have a coaxial constraint to an axis and an offset to the part next to them, both shown in red. I want them to constrain to the Z axis direction like the part in green.
When I try and constrain them to prevent them rotating around the axis I keep getting an over constrained message, I didn't have a problem with the other parts.
I created new planes and an axis throught the elbow in the direction I want to constrain to and that didn't work.
I am probably being stupid but some help would be appreciated, thank you.

 

[Oldbelt]

to many constrains, anti rotading use "show referance geometri" angle and tee

 

[Stu3d]

to many constrains, anti rotading use "show referance geometri" angle and tee

Thank you for your time.
I couldn't open your package because I am a cheapskate and haven't upgraded for a while but you gave me enough of a clue to resolve my issue.
I suspected my problem related to my parts having very few flat surfaces to use for constraints and turning on "show reference geometry" in the drop down menu gave me flat planes to work with, never used that before!
Thanks again.

 

[OTE_TheMissile]

Rule of thumb: always constrain to reference geometry whenever possible, and by association always try to design your parts to take advantage of reference geometry. They should always be your most reliable source of assembly constraint features.