FLEX-Drain 4" Black Female Coupler. It is used for joining 2 pieces of cut plastic corrugated pipe together and to adapt Flex Drain pipe to some wyes and tees to improve the fit and function of the overall system. Made of durable polypropylene, this coupler has a maximum working pressure of 70 psi and is corrosion resistant, making it suitable for underground use. Its push fit connection ensures a secure and easy installation, while the limited manufacturer's warranty provides peace of mind.