Well, i made some valve-blocks, which were driven with pressurized air up to 5 bar. Only one was not air-tight. The first attempts were printed at 100% infill, later versions at 50% with 3mm walls. I cut threads (~10mm) and sanded the sealing faces with wet sand paper. It all worked. And it was PLA. (But i have to admit, the last cases with ABS/ASA were cracky..)
Oh, and there was a vase, printed by someone at 3D-Hubs with Colorfabb XT on a UM2 with very thin walls (0,5mm) - no water on the table!