Gurgling sound coming from my tub and sink drain

I think those sounds are more or less common in RV's. what may be happening is this. For this discussion I will describe MY RV.

The kitchen sink drains into a line that goes across under the Floor (heated bay) to a T fitting where the bathroom lav T's in and then on to the gray tank

Water rushing past the "T" is sucking air in, just like air rushing through a carb sucks gasoline. This causes Gurgle if the air admittance valve does not open. Not really a problem.