I have perfored the bottoms of the four tins with small holes to let the water come out.
To seal the tins, I cut a plastic surface with the same diameter. These surfaces must have holes in the center to add more pipes which will be the connectors between tins and the pipes, so the size of these holes has to be the same as the connecting pipes.
Cutting the surfaces:
The connectors had been glued to the surfaces and the surfaces to the tins.
Building the arms:
The extremes of the connecting pipes that will be inside the pumping ones must have a special shape to avoid friction with the inner pipe.
Shape of the connector’s end: