Black tank.

[NSTS1470]

I have been getting a pretty constant smell in bathroom. We r seasonal and don't move. U clean the tank post dump with built in sprayer it came with. In the past my bathroom fan would not pull odors. But lately any time the fan is on it stinks. Could the vent pipe be clogged. And if so how do I clear it.

[JRTJH]

If the bathroom fan is on (yeah even that little bitty one) and you flush, the fan will usually pull odors from the tank into the bathroom. If it doesn't, then I'd be concerned that the vent stack may be plugged. It only takes a very small bit of suction from the fan to create a stink...

In fact, most any exhaust fan in the RV will create the same problem.

Solution: turn off the exhaust fan before flushing. (or put a box of clothespins next to the toilet)

[parkgirl]

Our toilet was all of a sudden causing a stink so I checked the trouble-shooting in the Dometic manual. They say their toilets should NOT stink and there are only two reasons why they might: the black tank is too full OR the vent pipe is clogged. Unfortunately, I could not find anywhere good info on unclogging the vent if it's not a roof vent/bird nest type issue. (You can google info on clearing the vent from the top). Since our trailer is new, I assumed somehow the vent got clogged from the bottom (toilet paper, etc. issue) but I couldn't find info on how to find where that vent enters or how to clean it out.

Turns out after a few more days, it became clear that the tank was too full. (Our gauges have not worked from the beginning.) I was surprised though that it would start to smell so badly a few days before being full. Now we'll have to be more careful, but still I'd like to know more about the venting, where it is, etc. I wish they'd give us a schematic of the whole insides of the trailer. It sure would help.

Anyway, sounds like it's probably your vent, so I hope you get some answers here!
parkgirl

[Festus2]

Typically, vent pipes extend from the black water tank to the roof. The vent should protrude only a very small distance into the tank when installed properly. You can inspect the vent pipe, by removing the roof vent cap and shining a flashlight into the pipe. You may not be able to see much but any debris near the top end of the pipe should be visible. If you spot debris close to the roof, try using a coat hanger or something similar to pull it out.
If this doesn't get rid of the odor or improve the flushing, the debris may be lodged further on down and will require either a longer "snake". You may end up having to flush the debris down into the tank but if it isn't biodegradable, any debris may then become lodged in the drain pipe or valves. Pulling it up and out would probably be the best bet.
Pushing a long, thin probe down into the vent from above might give you a hint if anything is stuck in the pipe vent.

[SLIMSHADIE]

I thought my vent pipe was clogged one time too, the fan would pull the odor up after a flush. I didnt really mess with it till I got home, more tools. So I went to the roof and couldnt really get the cap off, thinking I was going to break it. Now what to do, I stuck my nose next to the cap and WOW it stunk. Well its working and the tanks were empty too. So a few days before the next trip I thru in a gallon of bleach and filled the black tank. When we got to camp, I emptied the tank and it was pretty dirty. Did that a few more times, after a few more trips and the odor pretty much went away. Thinking back, that year it seemed we hardly had sewer hookups on site. So I could hardly ever use the black tank flush it came with.