We installed two new Kohler toilets at different times. Now the water in one leaks out when the other is flushed. It never did before when we had one new one and one old on. Kohler tells us we need to put in a wye for the drain. We had two different plumbing people tell us that the system is sucking air. Which is correct?
Are you saying when you flush one it sucks the water out of the other one? It sounds like a venting issue.