Is there any reason I would not want to tie a new washing machine into a bathtub drain as long as I give the washing machine its own P trap? One plumber I spoke with was concerned the force of the washing machine "would suck the water right out of the trap" of the bathtub. Does that sound right? The washing machine is a high efficiency model and uses very little water. Also, can I use an AAV to vent the washing machine?