We have been smelling waste water gas/oders under the kitchen sink. Often when cabinet doors are shut. I lolled under sink just now and it stunk! No drips or leaks in pipes. But did notice there is NO pee-trap in either sink drain lines. It appears the Oder is just drifting up from the grey water tank. Is that my problem? Do you think there is a pee-trap under floor before it gets into tank?