i have electric heads fore and aft. The bow cabin opens to the head. There is an acrid smell in the head and the cabin. I sealed the bowl with plastic wrap and the smell dimenished noticeably. The other head has no smell and no bad smells come out the vent with a flush. We keep the tank empty since it required a repair last year. I recently replaced the pump macerator last fall. I am not sure what all this means but I feel it is a head issue. Has anyone been through this? OB