Sewer smell coming from under sink cabinet

[3330]

This has probably been well covered here but when I searched all I came up with were threads that talked about cracked holding tanks and mis-routed plumbing.

A couple night's back I was sitting at the desk which is right beside the sink island when I smelled sewer gas. This is significant because I no longer have much of a sense of smell. I determined that it was indeed coming from the space inside the cabinet but in checking the plumbing and even removing the vent cap that screws into the pipe to make sure the flap was doing it's job the only think I could think is that we are getting gas in from the sewer where we are hooked in with a full hookup deal.

I have been leaving my gray water valves open and the black water valve closed, just dumping it about once a week. For a trial I went out and closed the gray water valves and went to bed. The next morning and since then the smell is gone. Verified by the missus that can still smell very well.

I'm not sure how the gas got through the traps and not sure it did as the smell was strongest under the cabinet. Maybe I should replace the vent to make sure.

Anyway, I'm glad we got rid of that smell and thought I would just mention it in case it helps anyone else.

[3'senough]

A simple fix is to add a trap in your sewer hose by forming a "u" just before the hose goes into the hookup at the CS. This will act as the main trap for the entire unit much like your house has before going to the exterior connections. Your gray tanks will fill with gas otherwise. Leave the gray open and run your water to prefill it after hookup with a few gallons of water.

[lx22f/c]

Originally Posted by 3'senough

A simple fix is to add a trap in your sewer hose by forming a "u" just before the hose goes into the hookup at the CS. This will act as the main trap for the entire unit much like your house has before going to the exterior connections. Your gray tanks will fill with gas otherwise. Leave the gray open and run your water to prefill it after hookup with a few gallons of water.

X3

[Mustang65]

Under each of your sinks there is a vent connected to your drain pipe. This vent opens/closes, (as needed) to keep the draining water flowing and to keep a vacuum from forming in the gray water pipe. Unfortunately, the smell escapes from the vent when the air pressure inside of the TT is less than the outside air pressure (ceiling fan running with no window open, and possibly the heating/AC system running). This seems to be a flaw in the design of the vent. The best thing to do is keep a window cracked if the ceiling fan is on. I got tired of the daily odor and taped the bathroom sink pipe vent closed. There is no harm caused by this, and there is no difference in the rate of water draining from the sink or bath tub, or when draining the GRAY water tank. I know that this is not a recommended fix, but since then, I have not had an odor problem. It works for me. If the DW is happy, so I am happy!
Don

[eldermike]

Good advise so far, if you want to leave your grey open you need to form your hose to provide a liquid seal between you and the sewer (that's what a trap does).

[3330]

Yes it is all good advise, thanks guys.

I found that those anti siphoning vent devices are only a few bucks so I will pick up a couple when I'm at the store and replace both in this RV.

I've come to like the idea of leaving the gray water valves closed and dumping every few days too. This rig has one valve that leaks a bit and I think it's because it sat for years with the valves open. Also kind of like the idea of not having a continuously open path to the city sewer system. Although that's the case in permanent homes isn't it.

Now I have a title other than old man too. I'm the official valve opener on Saturday and Wednesday:wink:

[Jagiven]

My guess is sewer gas from the full hookups was backing up into your sewer system. The tip about creating a little P-trap with the sewer hose is good. What I have found; if the bathroom roof vent is on, it can pull air into the bathroom through the sewer’s roof vent or the sewer connection in your case and then pulls the odors into the room through a P-Trap that does not have enough water in it. Our shower drain is notorious for this issue, as it sloshes the water out as we travel.

I have looked at those little vacuum breaks and they are built very cheaply. It appears that they could easily stick slightly partially open allowing the odors to be released into the cabinets.