150mm Twinwall Coupler. If a Sealed Carrier System is Required Use 2 Seals per JointTWINWALLTwinwall drainage is predominantly used in stormwater applications where the strength of the pipe is key, such as under roads, sports pitches and landscaped areas. Because of their high compressive strength they can also be buried much deeper than standard PVC drainage pipes as they can easily support a greater weight of soil backfill.There are two options when connecting fittings to twinwall pipes andndash; they can either be loose jointed or sealed joints. Sealed joints, used with unperforated twinwall pipes in stormwater drainage applications, require separate seals to be inserted over the pipe prior to the fitting being connected. Loose joints (used with perforated twinwall pipes in land drain applications) use the same fittings but without the need for the rubber seal, allowing more rainwater to be collected into the pipes at the joint location.Twinwall pipes are made from HDPE (high density polyethylene). The outer ribs add compressive strength whilst the smooth inner bore promotes a friction-free flow of water.To cut twinwall pipes, just use one of the ribs as a guide and cut with a standard handsaw.