While taking a shower, our kitchen sink started filling up. The shower drain did not back up, and the grey tank was near empty. And a couple of others times while taking showers, the kitchen sink seemed to have a large bubble burst up from the drain. Also, there is a leak somewhere beneath the floor that seem to coincide with those events. There is no leak anywhere inside the trailer. Tomorrow I'm going to cut open the underbelly cloth and try to find the source of the leak. But does anyone have ideas as to what is going on? Thanks in advance.