The replacement for the Swimline 8-Foot Double Water Tube is made specifically for use with your rectangular or oval pool cover to eliminate stress on your pool and the cover. It's 33% heavier than other water bags, making it super durable - plus its valves are easy to fill up with a garden hose. This replacement for the Swimline water tube is best used with in-ground pool covers. Covering your pool with a winter cover keeps out dirt and debris, and this water tube helps keep the cover in place.1 buy = 24 tubes!