A 2" glue in straight fitting with integrated air bleed screw. Once mounted into plumbing this allows for effective bleeding of the system to help prime your equipment before start up

This fitting would normally be mounted just after the pump discharge where an air trap could cause the pump difficulty to prime. 

Other places you may require to bleed your system would be at the inline cartridge filter. The air bleed fitting should be installed in the highest part of that plumbing section.

This is a Spigot x Socket Fitting (Male x Female)

Top Tip

Test fit your plumbing first (dry fit) before final gluing. Best to use a plumbing cleaner first then solvent cement.