5 and 4 are the only ones getting water other than 1 and 2. 3 has a solid line blocking the flow into it, and even if that wasn’t there, since 4 has a hole/drain in the bottom and 5 can overflow, 3 can’t fill enough to reach the outflow. 5 is the only one that can fill up.
This is assuming this is a cross section of something 3d and not something 2d otherwise air packets would get trapped and prevent some of this.
5 and 4 are the only ones getting water other than 1 and 2. 3 has a solid line blocking the flow into it, and even if that wasn’t there, since 4 has a hole/drain in the bottom and 5 can overflow, 3 can’t fill enough to reach the outflow. 5 is the only one that can fill up.
Wrong! The room will begin filling with water from the overflow!
Just pick this up and put it into a tub. Now they’re all full. Take that math!
But which first
If they bothered to drill a drain into #4, I’m sure there is a floor drain.
I’m viewing the edges of the picture as impermeable.