1 will fill til it reaches the pipe 3 will start filling, it can’t get to 4 as there is no hole to the pipe to 4 3 will thus fill to the pipe which is a dead end 3 will continue filling I’ll let you work out the rest.
Cup 1 will start discharging, through its lower outlet pipe, into cup 3.
Cup 3's lower outlet will start discharging into cup 4 before it starts discharging into cup 5.