How to diagnose where septic odor is coming from ?

**miketinternet** · 03-22-2011, 06:40 AM

I have a toilet, sink and tub running left to right in a small bathroom and we are getting a sewer gas smell in the bathroom. It seems like after a tub drains with the exhaust fan on to remove the moisture it is much stronger. The rest of the time it is a faint smell. My first guess was some kind of blockage in the vent was sucking the trap dry in the tub but even when I add water after the tub is drained to fill the trap we get the smell.

I thought it was the toilet but I had that pulled and reset and even put silicone around the base. I am not sure if it is the tub or the toilet and was wondering how to trouble shoot it. Should I put a rag in the tub for a day or two to see if it is the tub or is there some other method ? The thing with the vent clog, wouldn't it happen with other drains tied into it or is it the lowest trap that gets emptied.

Any help is appreciated, thank you in advance

**Inspektor Ludwig** · 03-22-2011, 08:31 PM

First thing is put your nose right down into that tub drain. It'll be pretty strong so there would no mistaking where it's coming from. If it's not the tub then try the sink drain and under the sink and around the toilet. If the smell gets stronger with the fan on, then turn it on and you may be able to feel for air flow over the drains. If you can smell and feel the air coming out of a drain then something is causing your trap to siphon, could be lack of vent or lack of trap for that matter, lack of proper vent or "S" trap, studor vent, trap larger than trap arm, tailpiece too long, plugged drain etc. Did you recently remodel or buy a house that has been remodeled? If it's an older home you could have a broken pipe under a slab, or a pipe that has just been left open or abandoned in the wall. There's dozens of reasons but a good start would be to determine the age of the home and if any renovations took place since the home was built and in what fixture or approximate area the smell is coming from.

**miketinternet** · 03-23-2011, 05:30 AM

The house was built in 1965 and the bathroom was remodeled about 6 years ago. The only thing recent was a toilet replacement for a better flushing toilet. The whole job was properly permitted, inspected etc... 6 years ago so I think the venting is fine.

The smell is just a recent problem that I thought was related to the toilet and a broken seal but that has all been replaced and I put silicone around the base so I would think that is eliminated unless a toilet somehow can leak odor from anywhere other than the base.

If it was done wrong with all the items you list wouldn't it smell from the begining 6 years ago? This is more a recent thing so I am wondering if the vent is more of the issue with some sort of clog. The thing with the vent clog, wouldn't you get siphoning from other drains also?

**Inspektor Ludwig** · 03-23-2011, 08:46 PM

Were you able to find the area of the smell? Did you check your traps first? A trap can siphon if there is something plugging it downstream, but you should be able to tell which trap is dry if that was the case and yes, if something wasn't draining properly you could siphon other traps but I usually only see that happen when vents are either non-existent or installed incorrectly not so much with a plug. Plugs and siphoned traps are usually limited to the one fixture . What I'm saying is that sewer gas can only get into your bathroom by a dry trap, a broken pipe, an open pipe, a studor vent or in the case of your toilet maybe the flange cracked or the seal wasn't complete. You've got to narrow it down a bit in order to troubleshoot the problem. Do you have other plumbing fixtures above or below that maybe haven't been used in a while? It could be coming from somewhere close by, an old floor drain in the basement, a clean out..or even a vent pipe that is blowing downwind or near a window, how close is the exhaust fan termination to the vents on the roof? I don't think that a high powered exhaust fan combined with tight construction, such as no space under the door, would be able to cause enough negative pressure to pull air through a trap but I've seen stranger things, something to consider......

**Gsalet** · 03-23-2011, 09:09 PM

Something I have done that works, wait till the house is quiet, turn the water on in the kitchen. now sit on the bathroom floor with the fan off....... see if you can hear water running?? if you hear water running from the toilet that's the problem, from the tub that's the problem. You get the idea. This is a good place to start, my next step would be to use a smoke test. Good Luck

**johnjh2o1** · 03-24-2011, 05:14 AM

If the house was built in 1965 chances are the waste and vent lines a copper. It can be that it is a light weight copper. (DWV) If so it may be breaking down a this point in time. I have seen this happen on both waste and vent lines.

John

**miketinternet** · 03-24-2011, 06:14 AM

From what I can tell it is the tub drain. I put a rag into the drain and taped plastic over the knob for the drain to seal it and see if the smell goes away and confirm the problem.

The exhaust vent is in the ceiling and runs through the joists to a vent probably 10-12 feet out of the side of the house.

Is this something that is common and can be snaked from the roof ? I am getting the feeling that local plumbers are not too interested in the work due to the lack of call backs so I was wondering if one of those drain cleaner companies is more experienced with this type of stuff.

**LLigetfa** · 03-24-2011, 07:37 AM

If the cause is an improper vent and not a plugged vent, no amount of snaking will fix it. As for the exhaust fan, is there sufficient makeup air to not depressurize the room? Is the CFM of the fan matched to the CU FT of the room? You may need to increase the gap under the door or cut a louver vent into the door.

**miketinternet** · 03-24-2011, 10:33 AM

The bathroom is 6-8 years old and only recently has the problem. It was properly inspected and permitted so I assume the vent is fine. I get a more faint smell with the fan off, when it is on and the door is closed it is much stronger when done when the tub drains. Not sure of the fan CFM but it is a standard heater/fan from Nutone and the bathroom is probably 8x6 feet or just under.

**ballvalve** · 03-24-2011, 12:17 PM

Did you plug the overflow also? If no, it was still open to the trap.

Have you used drano and later bleach to clean your tub drain and trap? And bleach down the overflow? Might be a big snot ball of hair and yuk above water line causing stink.

And maybe your trap has a leak. Can you get under it?

How can a fan suck from the vent? It would have to pull the water out of the trap first.

Get out the maglite and have a look down into the tub drain. Water? Hair balls?

Plug the overflow and stick your shop vac in the drain - see if you get a slug of water out of the trap. If no, your trap leaks.

**miketinternet** · 03-24-2011, 01:49 PM

I don't know what you call it but it is a Whirlpool tub with a knob and a stopper that has a long metal rod attached to it that is sort of in a P shape. I pulled the stopper out and it is not a clear shot down the drain, there is a hole where the stopper bar goes in. There isn't an overflow, so I plugged the drain with a rag and taped plastic over the knob rather than disassemble it because that setup looks like one of those ships in a bottle to put back together. I figure in a day or two I will know if the smell is gone.

I have used draino in the past but not down the assembly where the knob is, I guess I could try that one.

The fan creates negative pressure, I think it is sucking septic gas up past the trap which is being siphoned off due to a clog or leak which I hope I don't have since it is in the slab.

I will try that shop vac one also, that is a good test to see if the trap is holding water. Thanks for your help

**Terry** · 03-24-2011, 03:43 PM

If you make sure the tub gets water occasionally, then there will be water in the trap.
Some of the large soaking tubs get used for planters and people forget to run a little water into them from time to time.

**ballvalve** · 03-24-2011, 06:26 PM

Whirlpool tubs are like front loading washers, they have all sorts of places for mold and slime and retch to grow and stink.

I would fill that tub and add a half gallon of 6% bleach and run the jets for 10 minutes, then add some dish soap and shut it down when it suds up.

Your smell is just mold in the lines, and I would forget about any plumbing issues.

But you must have a overflow somewhere....

**Inspektor Ludwig** · 03-25-2011, 08:30 PM

Ok so it's the tub, at least that's a start. I have seen a fan pull air through a trap but the fan was much bigger and the room was sealed pretty tight. Took a wee bit of effort to open the door. I've also seen traps on basement level fixtures "burp" sewer gas when AAVs are used, since they can't relieve the positive pressure coming down the stack. When someone upstairs flushes a toilet, the slug of water can blow a trap seal with a Studor on a lower fixture just enough to where a strong fan and tight construction will allow sewer gas to come out of the trap. If your significant other has long hair and loves to take baths.......well that's where I would start. Plug your overlfow drain and use the shop vac suggested earlier and if that doesn't work then it's time for the snake. 6 years of use.....should be quite a bit of hair. Oh yeah, decide how you want to tackle the plug first because you DON'T want to use Drano and THEN use the shop vac or snake. If you're going to use Drano use it as a last resort, you don't want to get that stuff anywhere near your skin (neighbor got a nasty burn and ruined a good pair of boots doing just that). Good Luck!