We recently had renos which included replacing a leaky outflow pipe. As it turns out, the air allowed out by the leaks was crucial to the functioning of a toilet at the back of our house, situated well away from the stack. Now that the pipe is air tight, the toilet overflows ocassionally, has consistently high water levels and poor flushing, and causes alarming bubbling noises in our kitchen sink. The wash machine, also in this bathroom, causes the bubbling in the kitchen sink as well. Our contractor recommended a pricey Japanese toilet that apparently has a strong enough flush to overcome the air pocket issue, but I don't like the idea of the bubbling persisting in the kitchen sink. I am seeing a plumber tomorrow, and was hoping someone would have some ideas about how to handle this problem before I throw myself at the plumber's mercy.

Thanks!