This is a diffuser bar I'm experimenting with to replace the outflow on a Fluval 207. Its a 17mm pipe. The end cap allows you to direct flow to the water surface for gas exchange. I printed with supports from the bed only. The pipe printed flat with holes up. The cap printed with closed end down. On one test there was a bit of ovalness in the open end where the cap goes and on another there was looseness. I fixed both but dipping the open end of the pipe in hot water from the microwave and fitting the cap.

If you want the pipe to open left, just mirror it in your slicer.