Lets see if you get this right.

@Scubaguy027 yay! Smart thinker!

@Scubaguy027 I think it’s 5 there’s an opening from 3 to 5 which will spill from 3 to 5 until 5 is filled and then 3 will fill once 5 and its opening are filled with water

@KaysHealingPath if you look at the tube from 3 to 5 the end is blocked

@Scubaguy027 1, 2, and 3 may never get filled depending on the flow rate. There are holes in the sides of each (the outlets) and the outlets that ARE LOWEST will drop water before outlets that are higher, so from 1 to 3 1st, then from 3 to 4 -- 4 fills first.

OOOhhh, I see the bloackages... I thought they were just bit-errors in the image.
so 4 and 5 and 6 never see any water...

@xmedleft nope 4 is blocked

@Scubaguy027 I missed that too!! 🤦🏻‍♀️🤣😂

@ScarletWitch thought it was 4 3 drains at the botom