I just did a test. I downloaded this hose nozzle from Thingiverse (http://www.thingiverse.com/thing:26730) and printed it with a layer height of .2 at a speed to 30mm. It has a fantastic stream but it leaks like crazy. I printed with no infill, i.e., a solid object.

To be fair, there is nothing scientific about my first test here and with a few more iterations, I may be able to figure out how to make it more watertight, but my initial feelings about 3d printed parts being used as plumbing parts, especially if they are mission critical or under pressure, are that you should be careful. An expensive commercial 3d printer may be able to make sufficient parts but our basic RepRap printers may not.

I used Pet+ to print this. It's possible that if I use ABS and then smooth it, the smoothing will seal it. I may try that later.

Here's a shot of mine in action. Maybe I'll use if for a "soaker"...lol....

Hose_Failure.jpg