Someone asked about waterers... that got me thinking. (Hubby just said 'uh oh, i'm in trouble now...' LOL)
I haven't made it yet, but have figured out the logistics (I think...) the waterer that is.
What the plan is...
use 3" or 4" pipe, with a screw on cap at the top, and either 2 - 90 degree fittings or one U shaped fitting, and a fitting to receive a screw on cap. **glue everything securely except the screw caps** you don't want it leaking!
then when you're filling it, cap it at the bottom. take off the top cap, fill with a hose. screw top cap back on, and take the one off the bottom. this way it's gravity fed, but relies on vacuum to keep from dumping it all out the bottom. then when the water level gets low, air will go back up the pipe and allow a bit more water out.
it's a similar concept to some parakeet/finch waterers i've had, but the trick here will be to keep shavings/food/etc from getting in and fouling the water supply further up the tube.
for more birds I guess you could also do a horizontal run similar to some of the feeders, but you would probably have to use a Y instead of U for the bend, and filling it would be a pain unless you found/made plugs for the holes to drink out of...
here's my idea roughly... but it's lacking the screw-on caps. sorry my image capabilities are a bit limited