Walsh
Are you certain the trap is even hooked up? Many times a trap is by accident left off the tub in haste, the waste will drain into the subsoil and go un-noticed for a long time. Have a look under there and see if the trap is even there. Aside from that, there are specific distances required between fittings on a sewer line to prevent the siphoning of a trap by the discharge of another fixture. WIthout seeing it, it is a shot in the dark to diagnose. Was the home built in an area that has inspection required of the plumbing contractor?
