Sewer Smell Outside Camper Opposite Tank HELP!

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New member
Jul 29, 2018
Help! We have a new to us 1997 Mallard by Fleetwood 25ft. We have been camping for several weeks now and just this past week noticed a distinct sewer Smell by the front corner near the tongue. The smell is not present anywhere else and comes and goes. We have cleaned the hot water heater to get rid of the sulfur smell and sanitized the water system. We have began trying to fill and clean the black tank. We have checked the sewer vent there is no odor. We also checked and it is not a propane leak. We are stumped where could the smell be coming from?!?!?
Grey water tank?? It can smell as bad or worse than the black tank. Each sink drain system has an air admittance valve somewhere in the system. It is usually hidden under a counter top, up high, and it has a valve in it. They do go bad from time to time allowing tank smells in where they should not be. Replacements can be purchased at any hardware store that carries plumbing stuff, they are not RV specific.

There is also an air vent in each tank which usually goes to roof. You may have one that is no long in the tank but may have pulled out or broken allowing fumes to exit the tank(s) at that level. You might be able to check that by using a hose and pouring water down the vent tube. It should go straight into the tank and not flush out around the tank onto the ground.
Is the smell outside or inside. I'm thinking the way you talk, it's outside so that would eliminate the air admittance valves. Fill the tanks up one at a time all the way to the top. Look down the toilet and when you see water coming up the pipe, stop filling. Let it sit for a couple of hours then do back and see if the water level dropped. If it did, you may see water dripping outside. It could be the joint where the vent pipe or the toilet pipe enters the tank. The seal could have been compromised. Do the same with the gray tank.
The smell is only outside so I do not think it is the air admittance valve. We hadn't considered the grey tank being the cause. We just did a thourough sanitize with bleach throughout the water system and enptied through the grey tank. Would that have cleaned it? We are currently watching the black as it's full with water and chemical we haven't found a leak yet. We will have to check the vent pipes next.
Are your propane tanks near where you smell it?  Sometimes slight whiffs of propane smell like dead animals.
You might be cooking a bad battery, does it have a sulfur smell? 
This is an excellent example for new RVers because you can never assume that something like a sewer smell really is the sewer.  The same is true of water leaks.  Water always seeks the lowest point so water coming out of an air conditioner vent may come from the front of the vehicle where the courtesy lights sometimes leak.  You had here five good things that might have caused the odor and it was the last one mentioned that was the culprit.

Glad you found the cause and, especially, that you reported back so others can benefit by your experience.

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