This is my skimmer, it was purchased from a LFS
but as you can see its just built from off-the-shelve PVC
fittings. The only thing I don't understand is how he made the venturi valve... I know air is being sucked in half way through the water intake (through that cactus arm looking thing), so there must be a venturi valve somewhere in the 3/4 inch PVC
T fitting. Water level inside the skimmer (to adjust how much foaming is ejected through the top collection cup) is controlled by the valve on the exhaust side (you can barely see it in the photo, on the bottom). Water is supplied via a Rio 600 pump (not shown), through the clear plastic hose.
So far this skimmer has been completely maintainance free, I have not ever cleaned it once (except the "upside down U" PVC
section that takes the slimmy stuff to the colletion cup) and it has been running for about 6 or 7 years now. The only draw back is that the bubble it forms are fairly large, some skimmers produce extremely fine bubbles which is more effective. However you might be able to fix it by using a better venturi valve, although with the fairly large bubbles mine still works very well - as visible from the stuff it spits out to the collection cup.
Hope that helps!