With thinner walls than Schedule 40 fittings, these are lighter in weight and have more space on the inside for high-flow applications, such as underground gravity-flow sewer and storm drainage lines. They are also known as SDR 35 fittings. Made of PVC, they have good strength and corrosion resistance. All meet an ASTM specification and testing requirement for material quality, dimensions, and workmanship.

To prevent leaks in threaded connections, apply a sealant to the male threads. Threaded connections can be taken apart as needed for maintenance and repair. For metal threads, use PTFE tape. For plastic threads, apply a non-hardening, plastic-compatible sealant. Tape or sealants with PTFE are not recommended for plastic-to-plastic connections. When making a threaded connection be careful not to overtighten the threads. To prevent cracks and leaks, finger tighten the fitting, then wrench-tighten one to two turns.

Warning: Never use plastic pipe fittings, flanges, and pipe with compressed air or gas.