Maybe these if you need to extend the pipe without making the slab/beam hole too much bigger:   Geberit 366.887.16.1 Hdpe Straight Connector £21.48 Tax included Geberit 366.887.16.1 HDPE Straight Connector 90mm - 90mm Ring seal socket Or   Geberit 367.887.16.1 Hdpe Straight Connector £21.48 Tax included Geberit 367.887.16.1 HD