as i've been messing around with various submarine entry room methods, i've noticed that a tunnel created between two turret rings is curiously prone to flooding the section that holds it, better still if the tunnel is a sealed room itself - it'll flood with water present in the section that holds the tunnel - with 0 fluid level reading, you'll drown.

essentially the setup i tried to make was;

• sealed room at the very bottom, meant to be the interior
• two tunnels, sharing a subgrid, connecting the topside to the interior (both sealed, hatches top and bottom, connected by valves.)
• a room that holds the tunnels, a pair of turret rings on top and bottom connected from main grid to the tunnel subgrid

curiously - on dry land - even if you completly filled the tunnel rooms with fluid, they'd appear entirely dry, even if the fluid meter reading would reach somewhere in the ballpark of 97% of their capacity.

the interior room remained dry, so long as you didn't dump the spawned invis-fluid from the tunnels into it.

https://steamcommunity.com/sharedfiles/filedetails/?id=2850736202

example build for refference