Pipe liners (or stiffeners as they are sometimes called) should always be used with compression style MDPE fittings. Liners are fitted inside the MDPE pipe to add rigidity to the pipe wall when the fitting is compressed to make the seal.
MDPE Pipe - 25mm x 50mtr Black
MDPE Pipe - 25mm x 25mtr Blue
MDPE Pipe - 25mm x 100mtr Blue
MDPE Gas Pipe - 32mm x 100mtr Yellow
MDPE Gas Pipe - 25mm x 100mtr Yellow
Durable Pipe Plug for Rowing Machine Indoor Rower End Cap Outer Pipe Plug