[DQDick]

First of all your rig isn't totally equipped with P traps. Your shower, for instance, has a funny substitue for one that can become clogged and be slightly open and your kitchen sink has a valve that can stick open. The shower thing is located on the ceiling in my basement and it is supposed to function as a replacement for a P trap. Ours got crud in it that kept it slightly open and so we replaced it and started using a screen in the shower drain. That screen is an eye opener. The one under our kitchen sink is supposed to take the place of a vent pipe and is supposed to only open to let air in when you dump the sink water. It's just a plug on a spring, however, and can stick open leaving a path directly from the gray tank to your air.