Hooking up Suburban water heater - User Error

[Tailspin]

Hello,
I bought a suburban water heater to replace the one that someone had screwed a boat plug into the anode prior to me purchasing (thanks for helping me out w/ that one, wouldn't have figured out).
Now I have a different issue, water fills for a few minutes then sprays out the back of the tank. The PEX tubes are not cracked.

There was two adapters I took from the old tank. I was 99.7% sure I did not mix them up (not that it means anything, the old tank was shot anyway).
I put the adapters in the new tanks with the one with the valve (see photo) in the hot water (top of tank) so that water could come out, but not backflow.
I've attached the setup, there is a bypass valve at the bottom T intersection above the blue towel (see photo) but not at the top T.

Any help would be appreciated, assume I'm a moron because clearly I missed something because it doesn't work. I've probably missed the obvious somewhere.

[Herk7769]

Is the top check valve installed properly?

It is supposed to let water flow from the tank INTO the PEX and not allow water in the PEX to enter the tank from the top.

The bottom attachment is the open one. The T valve controls where the water is supposed to go (into the bottom of the tank OR up the cross tube into the hot water outlet PEX).

[Tailspin]

Yes, that is the way I installed it by looking at the old one.
Is it possible that it could have been airlocked or something?

When I connected the watersource to the RV it filled for a few minutes without issue then boom. Its just a garden hose type hookup, so the pressure shouldn't have been an issue or anything.

[Tailspin]

Ok, connected it back up, think I found the issue. This elbow is loose no matter how tight the connection to the tank gets. Somehow it must be broken or missing a seal from when I took out the rusted one.