PEX A to PVC Sch40 outside/buried

[cnb8869]

DIY'r here. I have a 3 year old home, built in 2020. Heavy clay. Off the road about 240'. When initially constructed, plumber took 1" PEX A, from inside the house, through the foundation (basement wall), and transitioned to 1 1/2" sch 40 PVC about 15' from the house (now underground), and took that 1 1/2" sch 40 pvc all the way to the meter. Fast forward 3 years -- the transition sch 80 pvc fitting broke, at the threads . PEX had brass male threads attached, into a sch 80 fitting, then glued to sch 40 1 1/2" PVC. The threads on the sch 80 fitting broke. I dug up and replaced. Was he wrong? Why did it fail? Did he just overtighten, or did settlement try to pull the pipes apart and failed the thread?
(ignore the larger 2" electrical conduit in picture..although it was in same trench)

 

[Breplum]

Even the plumbing code (UPC) states to NEVER, as in= "prohibited"use plastic female threads. ALWAYS use only MALE threads for transitions. I repeat this often on these forums: The installer was an idiot...of course it failed ! It was destined to fail because they are under physical forces pushing outward.
Though, frankly, male plastic also breaks readily because the threads create a weak spot. But, that is a different set of forces.
In cases of repeated breaking at threaded joints, we use a water heater flex to eliminate strain, then build up an access box that makes the joints permanently serviceable.

 

[Sponsor]

 

[John Gayewski]

We never use threaded connections underground. For copper we flare or braze. Plastic is all glue. There are pvc by pex adapters that should be used.