I had bought a 19" drip tray for my bar build, but didn't think to get one with a drain at the time. Well, I decided I was having none of that, so I added one (sorry there aren't more pictures).
1/4" NPT to 1/4" hose barb (<$4.00)
5 1/2" Washers (5@$0.20) (You can get away with a nut if you find someone at HomeDepot who can actually help you)
1/4" ID hose ()
1 sheet thin acrylic (<$2.00)
Silicone (I already had some)
Glue (Already had it)
The sheet of acrylic I bought was 8" wide. The drain was supposed to be 4", so I split the sheet in half, then took in one side until it dropped in. The two sheets overlapped, so I measured the overlap and subtracted half from each sheet.
I measured and marked the center of the tray and made a dent with a nail. I used a diamond bit to make the first hole and finished it off with a step bit. Because I didn't want any beer left in the tray, I used washers to recess the thread as much on the underside of the tray as possible, glued the washers together, and glued the barb to the washers. When it was dry, I used silicone to seal the hole.
To get the sheets to the right angle, I taped some painters tape to the side that would press up against the side and made it flush. Then I sealed along the long sides, waited for it to dry, removed the tape, and then sealed the final side. Finally, I sealed the edge that was raised by the drain, and leveled off the exposed metal part.
Lastly, I had to cut the grate that covers the tray. I found the center of the grate, and measured a line to the top of the corner. I used a dremel to cut the steel off.
Finally, I marked and made a hole in the bar and ran the hose. I was worried that 1/4" wouldn't drain fast enough. It does, though I would urge anyone doing this to think if they could accomodate a larger drain. If you can, you should. I did a water test to make sure no beer could get under the ramps I made (it did leak until I isolated the holes). It's working wonderfully now. I'll be draining the excess into a bucket of StarSan so that I can leave the bucket there and not worry about mold instead of emptying it constantly (which would defeat the purpose).
I'm sorry I didn't take any more pictures, but if anyone has questions or would like any extra pictures, I'd be happy to help.