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There's no water flooding from the upper vent like the others, maybe it's for air flow or drainage. It certainly looks less durable than the chamber door and is large enough to crawl through.
You ignite your lightsaber and hack away at the grate. Although it's hard to reach, you manage to smash it and a durasteel baffle behind it.
The cold water is up to your ribs now. You calm yourself, close your eyes, and extend your arm splaying your hand at T3M4. With the power of the force you levitate the droid up into the vent. Beeping rapidly in confusion as it lifts into the air.
With most of your weight underwater you easily hoist yourself up after him. With Kreia surmounting it shortly after when the water level reaches the grate.