Sometimes when someone flushes his toilet on the upper floors, pressure is created that can suck water from your toilet bowl into the sewage pipe. When that happens the water level in the bowl will drop so drastically that it leaves a gap in the "S" bend, allowing foul air from the sewage pipe to seep into your toilet.
So if your toilet smells bad, first check there is sufficient water in the toilet bowl. No, not in the cistern but in the toilet bowl itself. This water in the bowl acts as a barrier to foul air from the sewage pipe, and prevents any foul smell entering the toilet through the sewage pipe.
If the water level in the toilet bowl is high enough above the "S" bend, then you should suspect an unsealed pan collar as the culprit for the stink.
Now, what about the report that some people complained their toilets smelled after the HDB upgrading exercise?
I believe that had nothing to do with the replacement of the cast-iron sewage pipe nor with the removal of the air vent pipe. The reason for the stink was very likely due to the bad installation of their toilet bowl. It was likely cracks developed at the cement base of the toilet bowl when the sewage pipe was changed, and because the pan collar of the toilet was not properly sealed, foul air escaped from the sewage system into the toilet.
LESSON LEARNT:
Ensure your plumber applies a silicone seal around the pan collar when he first installs the toilet bowl. That is the proper and correct procedure to install the toilet bowl. In the west plumbers use a wax gasket to ensure an airtight seal between the toilet bowl and the sewage pipe.
Readers will recall that during the 2003 SARS epidermic, it was reported in Hongkong the virus spread from one floor to the floor below via the sewage pipe. Although details were not divulged in the press report, I suspect the leak was caused by improper toilet bowl installation.
When someone flushes his toilet on the upper floors, obviously the foul air carrying viruses and bacteria will be "flushed" into the toilet on the floor below through the unsealed pan collar. Hence the stink.
I would probably have remained ignorant today of how unsanitary my toilet installation was had I not experienced the stinky toilet bowl problem.
Now, even if you have a toilet bowl that is completely sealed so that no air could escape from the chamber once the toilet is cemented to the floor, it is still advisable to ask your plumber to apply silicone sealant to the pan collar. Otherwise you risk allowing viruses to enter your toilet each time someone on the upper floors flushes the toilet.
As we know, cement is porous and over time will develop cracks so that most people will find their toilets stink after some years, especially for those with unsealed pan collars. You can prevent the stink by getting your plumber to apply silicone sealant to the pan collar during the initial installation of the toilet bowl.
Why risk your family's health?
POSTSCRIPT: Public health was at risk so I posted the issue on a forum, see below:
A friend pm'ed me asking why apply silicone sealant when the plumber already used white cement to seal the toilet bowl to the floor?
Well, the silicone sealant is applied to the pan collar -- the piece that is connected to the sewage pipe hole. If the pan collar is not sealed, foul air (and soil too) will seep into yr toilet bowl chamber due to the air presure at work.
Like others, I did not ask my plumber to seal the pan collar when he first installed the bowl. After installation, my toilet smelled badly, particularly when someone on higher floors flushed the toilet.
My toilet was a 1-piece design, and had 2 rectangular holes at the back of the toilet bowl. Hence I could detect the foul smell. More importantly, I realized the risk I was putting my family to, breathing in bad air, particularly bacteria and viruses from sick neighbors upstairs after they had flushed the toilet.
If not for the toilet design I had chosen, I would not have detected the foul smell, and the problem probably would only surface several years later.
You don't get any foul smell if your toilet bowl has no openings and is fully sealed by the white cement onto the floor. But over time the cement will develop tiny cracks, that is when you begin to detect foul smell from the toilet bowl area. That happened to my old toilet (after 5 yrs), although at that time I did not know what caused the bad smell. Maybe the earthquakes from Indonesia over last 2 yrs was a contributory factor, causing tiny cracks in the cement to appear, thereby allowing foul air to seep into the toilet space?
Anyway, when my plumber told me he never applied silicone sealant to the pan collar I realized probably all plumbers in Singapore also install toilet bowls without applying silicone sealant!
That is very unhygienic. Ask yr plumber if that is true. Probably he will tell you he don't use silicone sealant for your toilet bowl's pan collar too.
With unsealed toilet bowls we are probably breathing in all sorts of viruses and bacteria discharged from sick neighbors in the block without knowing it.
The HK health authorities at first were mystified how the SARS virus were spreading in the same apartment block. Finally they traced the spread to faulty sewage pipe.
The authorities did not reveal what caused the leak (in order not to spread public panic) but the culprit was the unsealed toilet bowl that allowed foul air (carrying the virus) to spread from one upper flat to another lower down. If the toilet pipe had merely been leaking water, do you think the affected flat owner would not have noticed that and left the leak unattended? Of course not! So I believe SARS had spread via the unsealed toilet bowl pan collar!
Now that my toilet bowl has been re-installed, there is no more foul smell !
So, please remind yr plumber to apply silicone sealant to the pan collar.
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