[A strike]

“It is impossible for the front dome or aft to “come out” when there is 4000 psi pushing it inward. Sheese.”

Are you sure about that?
Can not a toothpaste tube pop off a cap if squeezed when outside pressures are equal ?

[Axenolith]

If you are squeezing it the pressure inside is higher. If you are squeezing it uniformly all over every surface then the surface will resist until some aspect of it’s construction reaches a failure point with respect to the contents ability to withstand compression.

[Bikkuri]

"Are you sure about that?
Can not a toothpaste tube pop off a cap if squeezed when outside pressures are equal ?"

Think about that.. you have to squeeze the tube (implode) before the cap is forced off.
If you never squeezed the tube, the cap won't move (unless it was mailed USPS /s).