I built a tank for a guy and used the stock bung and cap. Since I was so smart I just drilled a hole in the cap because I thought that would be sufficient. I used 16 ga steel and bungs I got from a hotrod shop and barbed fittings you can get anywhere. Feed was on the bottom, return toward the top on the front.

Sure enough - he brought it back a couple of days later, oil all over the rear half of the bike. The cap blew off and apparently his wife was riding with him and she doesn't like me too much now. I ended up welding in another bung and fitting and venting it to the scavenging port on the back of the engine.

After reading more on the subject the only change I would have made would have been to weld a baffle under the return to prevent air bubbles. Next time I'll do that.