I live in a 1500 sq ft house in the South. Last night I washed dishes during a rainstorm. Later I was awoken by a nasty smell of sewage. The smell was strongest in the master bedroom/bath, but permeated the whole house. I opened some windows turned on the ceiling fan and got rid of the worst of it. I then went back to sleep.

This has happened once before. During a period when I wasn't using the master bedroom, the sewer trap in the toilet went dry and some gas got back into the room. A couple of flushes fixed that problem, but when I checked last night the trap was fine.

A few other clues: Once or twice during heavy rains I've experienced backflow into the toilets when flushing. I also had to have a plumber come out a few months ago when the septic line became completely clogged to clean it out. I also know the former owner had to have some septic field work done, but I don't know the extent of the work.

As far as I know I only have one tank, one building on that tank and no pumps anywhere in the septic system.

What is the likely cause of this? Where should I start looking for a cause?

 

You've mentioned a problem with every part of your drain system. The problem could be almost any of the things you mentioned. Drain lines don't normally clog, there is a reason somewhere. Then there is the toilet trap being sucked out which points to a plumbing problem, either a missing vent or clogged lines. The smell could be caused by something as simple as a leaking wax seal underneath the toilet.

 

Well to start with the simpler part of the problem, is there a way to check the toilet seal non-destructively? I haven't noticed any signs of water leakage.

As for the larger issues, what would be the best way to assess my plumbing and septic systems? Call a home inspector for a general overview? A plumber ($$$) to check the sewage lines? Or a septic company to check the tank and field?

 

That clue leads me to believe your experiencing a septic tank/field issue.

First question, have you had the tank pumped recently, the guys that do that can pretty clearly identify issue just from the situation in the tank.

It sounds like your tank is not emptying into the fields, we can only guess why!

 

Does your house have a basement or crawl space? If so go below the toilet so you can see the drain pipe. You might see it leaking. Other than that there isn't an easy way to test the wax seal so if it is suspected to be a problem it gets replaced. The wax rings are only a couple dollars.

As for your septic system you need to find an expert or someone experienced in your area. You do not want the average septic pump truck driver but someone good at finding and diagnosing problems. That could be someone at a septic pumping company, a septic installation contractor, or possibly a inspector. It just depends on who's in your area. A general plumber can help with the piping inside your home but most don't deal too much with failing/problem septic systems.

 

A couple of updates here. The previous owner had not bothered to bolt the toilet down! I’ve put a couple of wing nuts on it as a preventative measure. But last night we got heavy rains again, and once again the house got smelly.

Called my home warranty company but they didn’t have a local septic contractor, so they authorized me to find a 3rd party contractor. Just sent out a couple on inquiries but no response yet.

I’ve read on some state run websites that in flood prone areas it is advised to install a backflow valve. Any chance that would help my stinky situation?

 

Back flow preventers are not generally not used on septic systems. In that application they are more trouble than they are worth.

 

Sorry to raise this old post from the dead, but I wanted to follow up on this as I now have a bit more time and money to try and resolve this. Since my last post, I have not had a recurrence of the smell, but I figure it's only a matter of time ... and weather.

@Pilot Dane can you expand a bit on why backflow preventers are "more trouble than they are worth?" It'd be worth a lot of trouble to prevent that godawful smell.

A few more data points on my situation. I have noticed that at least one, perhaps more, of my sinks doesn't have a p-trap. This seems very odd, and was noted as a possible source of sewer gas. Another thing that was mentioned was clogged gutters potentially causing an issue, and it's been quite a while since they've been cleared out. That said, I really don't understand how clogged gutters could trigger the release of sewer gas into the house.

 

Backflow valves are used when connected to city sewer. They prevent massive backflows into your house or basement if the sewer main clogs. With the very low flow rate and volume of a home septic system they tend to collect debris and clog, and they often don't work when needed (leak).

 

Gutter and downspout water must not be piped into the septic tank.

If you can see wastewater backing up into the toilet then any imperfection in the wax ring under the toilet can result in wastewater leaking out onto the floor.

 

Two things stand out BIG time.

One, the sucking out of the toilet albeit only one or two times. And second the statement that you have no traps on any of your sinks!

Resolve those two problems and I'm betting the smell problem will be eliminated. Check out the vent situation. Is it clogged or not big enought or maybe not located in the right place or maybe you need another one. And install traps on ALL sewer or drain items.
And pleasae remove toilet and reinstall proberly.