Versatile Modular tubing is rigid yet flexible for customized aquarium plumbing applications. The durable, rigid modular hoses are segmented to flex and bend into angles and curves you need to direct water flow, and standard measurements make assembly and installation a snap. These black plastic pieces snap together with other modular pieces. They are for use inside an aquarium or sump, since they just snap together, they are not leak proof. The round nozzle creates a jet flow.