I believe this design is the same as is depicted in the master WFC system shown here
as you can see there is a water tank above the stacked cells, that allows water to down flow into the cells by gravity, and the gas to bubble up through the water tank, acting as a bubbler as well
this is exactly what we see in this photo
there is a water chamber above the stack, and a tube to act like a bubbler, the gases rise to the top and then flow into the gas processor
