Anti-Vortex bulk head assembly.
Need to prevent drawing air into your pump? This device will do that.
Install in the bottom of your tank, where the normal bulkhead fitting goes, and you will not be pulling air into your pump through the suction line because this device prevents vortexing (which causes you to draw air into a pump).
They come in for sizes, 1", 1 1/4" 1 1/2"and 2" The sizes refer to the male NPT (national pipe thread). You can attach your fittings to thread to supply your pump.
The anti-vortex fittings include a gasket and a flynut but Rittenhouse recommends that you apply a little bit of silicon sealant to help prevent any leaks.