A device is provided for connecting pipe parts between two compartments of a filtration unit for water of a swimming pool. The filtration unit has a filtration compartment submerged in the water and equipped with at least one filtration means and a pumping compartment situated outside of the swimming pool and equipped with at least one suction and return pump. The compartments are connected by a common part that straddles the walls of the swimming pool. The filtration means and pump or pumps are connected in combination with suction and return pipe parts, which have one part situated in the filtration compartment and one part situated in the pumping compartment. At the common connecting part, watertight connecting members are positioned between the suction and return pipe conduit parts, whose thickness is less than the diameter of the various pipe parts.