I've just had my house replumbed at great expense but am in dispute with the plumber over the bathroom plumbing. Basically the bath, basin and toilet all send waste out to the soil and vent which is different to my old house where bath and basin sent their waste down the rainwater pipe. My concern is that flushing the toilet or some other as yet unknown event will cause the seals in the traps to be vacuumed out with obvious unpleasant consequences. To give more detail, the bath goes directly into the stack at about the same height as and adjacent to where the toilet waste goes in. In fact the toilet waste travels horizontally across the outside wall for about three or four feet (slight slope). It's into this horizontal waste pipe that the basin waste drops into, rather than directly into the stack. So is this illegal or even imorral?