I see your point. The only protection you'd have would be the check valve, A "P" trap's simply added protection. Also when you transition from the vertical to the horizontal I'd use a short sweep in place of a regular elbo. Good luck, TomQuote:
why would I need a P-trap here? I realize it probably doesn't do any harm, but since it's a closed system, wouldn't it be impossible for sewer gases to escape?
