Maybe submerge the unit into water, and try. Or maybe point the bottom to the ceiling, and see if that change things.However it comes without any directional info. Could it be possible that a heat trap can work on either side? Bi directional? I can blow through either side, it does seem though that one end has less restriction than the other but that is my first impression?
There is only one nipple that is an OEM replacement. They do not have a specific direction they flow in, no clor code or arrow, so the one unit they sell is suppose to be used on the hot or cold water side contrary to what I have seen from other manufactures and older Rheem replacement parts. (aka the ball valve / check valve scenario)
They said go ahead and use this unit on either side, the water should flow bi directionally and there is not one direction the water is suppose to flow.
If you had answered no, then you could have saved time on the phone.Your piece has stuff down the middle, right?