The tanks of the " Opt Betholit " series are made of a unique material composition which is high quality, enviroment friendly and durable(Available in vehicle access and pedestrian access version) . We are so convinced on the quality of this product that we give a 15 year warranty ( premise is a professional and competent installation) on them. The rotation method of production ( made in one piece) underlines the durability and life long expectation on these tanks. all tanks are equiped as a matter of course with a child safe lid.The 1300L tank can be used under or overground , The 3500L and 5000L tanks are suitable for underground installation( max Burial Depth 80cm.) With underground installation a vertical shaft extension is usually required.All tanks are well prepared for the necesary accessoires, ensuering a quick and problem free installation.The tanks can be connected together using the integrated connection socket , to allow all required volumes A tried and tested product with a wide range of sizes to fit all needs.