PVC 90 degree tees are designed to link three pieces of UPVC pipe together at right angles to each other.
The flow characteristics of a PVC Tee are different depending which branch of the tee the fluid is entering and leaving. If going straight through, the friction loss is quite low (slightly more than a straight piece of pipe) but when the fluid is passing through 90 degrees (in or out the branch), friction loss is much greater than that. The plain 90 degree tee has solvent cement sockets at either end. The PVC 90 degree tees have a pressure rating of greater than 10bar and are fully WRAS approved for use with drinking water.