I have a ground floor bathroom. 2 wastepipes run to an open gully trap outside. The washing machine is connected to the bath waste upstream of it. The pipes used to terminate below the water level in the gully trap but the gurgling drove me mad so i chopped them off just above it. We now get bad drain smells at random times in the room. any ideas please? I'm not sure if shortening the pipes outside has anything to do with it or not. It was about a month later that the smell started. Thanks.