On 7/14/2026 at 8:28 PM, Crossy said:

There "should" be a vent to the outside at the top of the soil pipe, ours is just an open pipe in the wall.

If the local wildlife has made its home in there it could stop the gases from the tank venting out and instead coming into the room.

Wouldn't you have a mesh cover to stop uninvited guests blocking the airway?

7 minutes ago, Photoguy21 said:

Wouldn't you have a mesh cover to stop uninvited guests blocking the airway?

I made one out of mosquito wire mesh, so yes, it is smart to have something more than just a hat sitting on top of the pipe.

3 minutes ago, Hummin said:

I made one out of mosquito wire mesh, so yes, it is smart to have something more than just a hat sitting on top of the pipe.

Just a bit of mesh to cover the open end of the pipe that is enough

If it is not a proper water lock in the shower drain, it will come smell from the septic.

Just now, Geir Rasch said:

If it is not a proper water lock in the shower drain, it will come smell from the septic.

We have separate septic tanks for the toilets, apart from the household wastewater system. We still get some smell from the vent system in our second floor toilet, depending on the weather, temperature and wind.

30 minutes ago, Hummin said:

If you want to get rid of the smell, you need to redesign your plumbing, or live with the smell.

Respectfully where did I say there was a smell I needed to remove?

You initially replied to my question directed at another poster about never having had the septic cleared out........

8 minutes ago, topt said:

Respectfully where did I say there was a smell I needed to remove?

You initially replied to my question directed at another poster about never having had the septic cleared out........

Sorry, I did mistake you for OP for some reason. Time difference, world cup, early morning ;-)

The system should be pressure less. Positive pressure could escape in p traps, if pressure is "high" enough.

Doesnt have to be in bars. If one p trap is low holding water, it can easily bubble up.

A ptrap could have a rip and water is lost in it and level too low. See if you can find evidence of faulty ptrap right beneath it. dried up water spots.

So you could try to manually fill up the ptraps regular and see if the smell will be gone. Not many in bathroom, you have sink and shower, bath?

Still smell? Then maybe toilet. NO more smell then one of the ptraps.

Also a negative pressure is possible, but then you should be connected to large drain system. It can suck out water from ptraps

and then level is slightly down and lock is gone, ejecteur working. Ptraps should be made with enough water lock.

The system should be atmospheric. So is your vent pipe not (partially) blocked?

Evaporation of water, but that takes more time, but in combination maybe with a tiny leak?

The tiniest ptrap would be in the shower. The lit in the floor, so the most vulnerable. Maybe 3 or less cm high.

Of course , the toilet, is it still closed or not? Seal ring or otherwise a wall of plaster inside still good?

You dont see and have to remove toilet from place, but if you lift and it has wall of plaster, you do need to make it new again.

Thats the old way of mounting toilets. Or you have to see if you can make connection new way with rubber seal rings.

My house here has system like shown on drawing, but in very very rare situations like heavy rain, do have smell and so level of ptrap too low.

If I leave house for months, I will close up the drains. Even put some vegetable oil in toilets, at least no evaporation of water in time.

Dont like to be surprised, coming home, and smell is coming to me. Welcome home.

On 7/15/2026 at 9:40 PM, topt said:

Not sure how you classify 'modern'?

Curious though as I have seen many comments on here over the years about people never having emptied their septic tank. The house I am in was built 18-20 years ago, and certainly in the last 16 years, the septic has never been emptied.

So is this abnormal?

Old style septic tanks in Thailand are usually concrete style tanks that fill up over time and therefore a sewage truck must attend and pump out the poo, fluids etc. "Modern" systems are usually a round plastic tank with two chambers and an overflow valve. Microbes are supposed to break down most of the waste thereby reducing the frequency when it needs to be emptied. However, even a modern septic tanks need to be emptied every few years as microbes don't break down everything. Also, if you clean your toilet with germ killing agents regularly, you will upset the balance of the microbes and it all starts to stink because the affluent isn't broken down.

Although it has been illegal for over a decade to discharge the sewage overflow into public spaces, public gutters, or the road, people do it anyway. In my case, the house I currently live in, all plumbing was replaced and a new septic tank was installed last year. First, the bathroom flooded because the plumber did not install a vent pipe to help the grey water flow uninhibited onto the road (which is also illegal). After forcing the plumber to rectify this oversight, the bathroom no longer floods. Second, the undersized vent valve of the septic tank pushed odours back up through the pipes. I think it's called negative pressure. Thirdly, because the plumber couldn't work out how to connect the p-trap under the sink, he merely pushed a hose going from the sink to a blue pipe in the wall and wiped a wee bit of silicon around it. Therefore anything connected to the "new" plumbing had foul odours come back up through the drain. Before the ipgrade, there were no foul odours.

I've given up educating Thai tradespeople. They have an excuse for everything. If they don't have a comeback, they just ignore me and walk off. My latest project, I told them to put a minimum 2% fall on the new toilet pipes coming from upstairs. First, they tried to convince me that a 75mm diameter pipe for solid waste was standard. Then they claimed that poo would magically be transported along a horizontal 7m long pipe without clogging.

Edited Thursday at 07:45 PM5 days by ZigM

2 hours ago, ZigM said:

Old style septic tanks in Thailand are usually concrete style tanks that fill up over time and therefore a sewage truck must attend and pump out the poo, fluids etc. "Modern" systems are usually a round plastic tank with two chambers and an overflow valve. Microbes are supposed to break down most of the waste thereby reducing the frequency when it needs to be emptied. However, even a modern septic tanks need to be emptied every few years as microbes don't break down everything. Also, if you clean your toilet with germ killing agents regularly, you will upset the balance of the microbes and it all starts to stink because the affluent isn't broken down.

Although it has been illegal for over a decade to discharge the sewage overflow into public spaces, public gutters, or the road, people do it anyway. In my case, the house I currently live in, all plumbing was replaced and a new septic tank was installed last year. First, the bathroom flooded because the plumber did not install a vent pipe to help the grey water flow uninhibited onto the road (which is also illegal). After forcing the plumber to rectify this oversight, the bathroom no longer floods. Second, the undersized vent valve of the septic tank pushed odours back up through the pipes. I think it's called negative pressure. Thirdly, because the plumber couldn't work out how to connect the p-trap under the sink, he merely pushed a hose going from the sink to a blue pipe in the wall and wiped a wee bit of silicon around it. Therefore anything connected to the "new" plumbing had foul odours come back up through the drain. Before the ipgrade, there were no foul odours.

I've given up educating Thai tradespeople. They have an excuse for everything. If they don't have a comeback, they just ignore me and walk off. My latest project, I told them to put a minimum 2% fall on the new toilet pipes coming from upstairs. First, they tried to convince me that a 75mm diameter pipe for solid waste was standard. Then they claimed that poo would magically be transported along a horizontal 7m long pipe without clogging.

It's frustrating but you get used to it.

I remember when tiling the roof I gave the roofer the destructions from the tile maker all in Thai with diagrams etc, he said 'we don't do it like that in Thailand'. :)