Thank you thank you thank you. Did not know about the vents. Went to Home Depot today and purchased two vents like these,
http://www.lowes.com/pd_24372-143-85539K_0__ for $2.92 each plus tax. Replaced in minutes. When I looked at my old ones the rubber had swelled and did not lay flat sealing the gases in the gray tank. While we did not have a major odor problem, when we turned on the overhead vent fans gas was also sucked out of the gray tank. Thank you again to the OP for asking and the posters that responded.
rocmoc n AZ/Mexico