https://docs.google.com/document/d/1HzhKG8yob8Zz50MvNLHzkewj8e9cIlVxImvjVuFewFw/edit?usp=sharing
Here's the doc from Mechtrauma's author. It'll help you understand

Ah I forget to mention oxygen station. Oxygen station automatically release oxygen when the air is thin in the hull, this will buy you some time when restarting oxygen supply. That's why I put it with diesel generator.

It's not leaking air. Diesel generator consumes air to make power, so the air in reactor room will keep going down until oxygen generator begins to work after 2 minutes. Only way to make through these 2 minutes is to put oxygen tanks in the generator to keep oxygen supply, don't let it stop because of lacking air. According to my test, 4-5 tanks will get you through. Every time you get reactor room flooded with water, diesel generator stops, and so will oxygen generator (well you should use your backup battery now to keep it running), you have to do this tank-filling task again.
So if you're playing a highly difficult campaign, and flood is quite frequent, you'd better use the nuclear reactor version. Using diesel fuel under water is really a bad idea to me.

S5000D keeps leaking air, and the oxygen station tank. what are we doing wrong?

Nice work! Added to the Mechtrauma shipyard.

🦅