Clean Check extendable backwater valves prevent sewage backup into a residence or building as a result of a plugged sewer system, excess volume in the system or groundwater flooding. They are designed to be installed easily outside a home, business or other structure, without using a costly manhole, and are readily accessible for maintenance or cleaning. The extendable valves consist of a tee-shaped valve body, a top collar and a bottom collar with a replaceable PVC flapper attached. In the event of back-pressure, the flapper blocks the reverse flow and prevents a sewage backup. Clean Check valves are available in ABS and PVC and in multiple sizes, to meet the needs of most residential and commercial construction. Vertical offset from upstream to downstream side is: 3 in and 4 in valves - 0.4 in, 6 in valve - 0.5 in.