Sewer odor in storage compartment

[TLG]

Just got back from 10 days at the beach with only minor issues that I was able to correct myself. But, every time I drained the black tanks there was a noticeable sewer odor in the front storage compartment. It became worse when I used the black tank flush. This occurred on both black tanks. There was no odor in the living area. My first guess was the check valves in the black tank flush lines, but I can't locate them. I assume they re in the underbelly somewhere. Every other 5th wheel we've had it was located under the bathroom sink. Anybody have a guess what the issue might be. At some point I'll be going to the dealer for whatever issues come up, but I'm thinking this might be one of those "can't duplicate the problem" situations. Thanks.

[DMRGMC]

We had a similiar problem with an odour that I was sure was black tank related. Did all the septic stuff adding chemical, flushing etc. When it persisted I was perplexed. The Navigator detected an odour outside at the battery door. We opened it to find that my oldest battery had shorted and charred as a result of one of the cells drying out. The battery was dated 2005 and that was last year, 2015, so 10 yrs old and well maintained.
I was sure it was septic odour in the basement area, Just a thought!

[troutslayer]

Generally, if the check valves are bad you will see water leaking. It could be a number of things, I suppose, but the first that comes to mind would be a loose fitting at the black tank vent pipe. As water is forced into the tank, from the rinser, some air would be forced out of the vent pipe (as long as toilet ball valve is closed). If there is a lose connection at the vent pipe base, you would be inclined to smell it in the basement area. Just "mind jamming" here .

[TLG]

Pretty sure its not the batteries. Unit is only a couple months old. But the loose vent pipe is highly possible. Can't find the check valves to see if they re leaking, but I would guess the odor would linger if there was a leak. It clears out as soon as I finish flushing the tanks. The odor appears when using both black tank flush systems. But, if they are both vented into one pipe, that could still be the answer. Thanks.