Lately I have been able to detect a musty odor when entering my 5th wheel.  It isn't noticeable outside near the hoses, but only indoors, sometimes stronger than others.  In trying to find out what could be the cause I ran across an article on blocked vents.  How would I find out if this is the cause?  Is it possible that falling leaves and debris blowing in the wind can block the vents?  I'd like to know if this is a possibility before I climb up on the roof.

I know the sensors aren't working all that well and I probably have some blockage at the bottom of the tank.  I'll be leaving my current location in four more days and plan to add some ice to the black tank to see if that will help clean the sensors.

gypsy

Gypsy, I know a lot of rv'ers don't like to use chemicals in their holding tanks. We have always used Thetford chemicals (primarily powdered). I usually dump in one packet each time after we dump the tank. We have never had odors. If the vent on the roof was clogged, you would get odors back in the RV, especially now that it's colder and the rig is closed up more. The vent has a little cap over it, so it would be tough to clog unless an insect has used it for a web or nest.

Thanks Bear, that's what I needed to know.  It is unlikely to be a clogged vent if there is a cap on it.  I use a packet every time I empty the tank, so the problem must be elsewhere.

Gypsy

In my opinion, the gray tank smells worse than the black. I would try cleaning your tanks using something like thetford level gauge cleaner. I find that stuff works good if you fill your tanks about 1/2 full, add the cleaner, then drive/move the rig. All that sloshing really helps clean them up.

That's an idea, Dan.  I will try to find it before I leave - there will be lots of sloshing opportunity before I even get out of the park!
Gypsy

We added one of the these and haven't had a problem since.  We don't even use any chemicals anymore.

I agree with NorCal Dan. I think the grey tanks smell worse than the black tanks. We have had success with pouring lemon scented Pine Sol down the black tanks occasionally.

I agree with the above, the gray water of the galley can get pretty rank.  About 2 times a year when the gray tank is about 1/2 full dump a cup of bleach down the drain let the tank continue to fill, dump as usual when full, that should help. I have not had an odor problem since I started doing it. 
 
Flyone

Check the air vent under the sinks on the grey water tank.  If it has failed, it might let smell back into the cabin.  This thing will look like an extension on a piece of PVC pipe, might be black.  The grey tank uses this vent to allow air inlet while dumping. 

Can you give us an idea of what to look for or how to tell if the vent has failed? I get an odor occasionally and suspect it's the vent under the sink, but I am at a loss for how to verify.

Well, I would find the vent by following the drain pipe.  It will go upward and have an enlargment of the pipe.  Should be black in color.  To determine if it is leaking or failed, you will have to remove it.  Should not be "glued on", but rather slip fitted.  If you can remove it, you will most likely see some debris of some kind between the seal and flapper. 

You may have to just replace it.  Should find it at a plumbing supply store (maybe at Home Depot or Lowe's). 

Hold on while I go check mine to see if it is removable

Yep, the top two inches unscrews.  Then a good rinse with running water will clear any debris (if that is the problem).  If not, should be a cheap fix.

Good Luck
Ken and Fran

It was more of a musty, even sweetish-like odor so I don't think it was from the black tank.  I do have a problem with the seal and even asked the NuWa folks to replace the seal for me.  They told me it didn't need replacing, but it's still doing the same thing.  When I flush I have to lift the pedal slightly upwards with my foot, or else the water drains completely out.  Then I depress the pedal on the right to add water to the bowl.  I need to get it looked at, but if the mfr can't take care of it then who do I get?
gypsy

So I crawled under the sink in the bathroom and found the air vent. Un-screwed it and looked it over and it appears to be fine. Any other idea's or places to look? When I do get a smell it is always confined to the bathroom. I might try placing a cover over the shower drain to see if that helps anything...used the sink drain plug on the sink to see if that helped and it didn't seem to make any difference. I'm starting to suspect the main vent pipe that goes to the roof via the linen closet in the bathroom, but, Monaco put in a false wall that hides most of it so getting to it is going to be near impossible...

On our coach at least, the black tank vent is a straight pipe to the roof, with a cap over it. I've cleaned it out a few times by removing the cover an putting a hose down to the bottom and flushing for a few minutes.