Drain Plug with hole for O-Ring

I made a few changes to the original, just added a grove for an o-ring. I used a 55mm O-ring from ebay:
http://www.ebay.com.au/itm/301745049935?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

It seals very well. You can change the size of the plug in the included SCAD file.

Check out the original drain plug for additional options.