Obviously, codes in the U.S. don't apply in your foreign country but they are based upon sound principles. If you don't have a building inspector or a code to follow, then you have a decision to make and then live with it. Just remember to keep a mop handy for washer overflows and a plunger and drain cleaner available for plugs. For inactive drains where the traps are siphoning and allowing sewer gas to come out, pour a littlbe bit of vegetable oil in the trap to keep it from evaporating. Good luck. By the way, what country are you in? We would be interested in knowing what type of building materials are used there. If I am guessing right from the jp on the end of your email address, then that sounds like nippon/japan. In that crowded country, I would think they are keenly interested in and have building and plumbing codes especially with the seismic activity they have and you mentioned. If all else fails, go to my favorite plumbing forum at www.plbg.com. The pro plumbers really get defensive and offensive about codes and any non-compliance.