I am drawing up plans for a small single story house I want built in Isaan later this year and am at the plumbing stage. For waste water the plan includes 1 bathroom (toilet, sink and floor drain for shower), one kitchen (sink) and laundry (washing machine, sink, and floor drain). The kitchen and laundry are on one side of house and the waste will go to the garden connected together (after a grease trap for the kitchen sink). The bathroom grey water (other side of house) will also go to the garden on a seperate line. The brown/black water from the toilet will go to a septic tank and then to an undecided sub terranian setup.

I have been reading up on venting and understand the concept (I think) but have been studying those free Thai government plans and notice the plans only show a 1 inch venting pipe coming from the septic tank, nowhere else? When I look around my rented house here in the city I see no pipes above the roof like I would commonly see in my home country where there always seem to be a few plus those things that look like a short vertical 8 inch pipe with connections for multiple grey water sources and a grate at ground level obviously for venting.

My question is where do the locals run their vent lines if none are visible on the roof? Why are there none on these plans except for the septic tank?

Our soil stack vents are through the outside wall just below the eaves rather than through the roof, easy as the loo is on the outside wall. Septic has its own vent.

Our soil stack vents are through the outside wall just below the eaves rather than through the roof, easy as the loo is on the outside wall. Septic has its own vent.

Thanks Crossy. So your stack is concealed inside the wall? What size pipe and I'm imagining a 90 degree elbow at the top with an exit hole in the wall under the eaves? Any cover/mesh over the hole?

Yup it's a 1 1/2" elbow on top of a buried pipe, there's a stainless tea-strainer arrangement over the end to discourage anything making it their home.

The stack itself runs under the bathroom floor and down inside a faux column to ground level. Not sure what size the soil pipe itself is.

you could follow the US or similar venting strategies for your vents - except that blackwater and greywater systems are piped separately here, so could have separate vents. In the West, they are combined, so you choose. note that vent outlets located near doors/windows can get aromatic at times, so distance is your friend, and a 1.5-2 meter would be a minimum separation I'd recommend.

generally, the strategy is that vents equalize air pressure within the pipework as water flows through it, preventing siphoning of fixture traps... to keep sewer gas out of occupied spaces. The 4" drain pipes used below floor for toilets obviate the need for a large vent stack, as they are large enough for air & water/waste to flow easily. I use 35mm/1 1/4" vent pipes tee-ing into the 4" toilet drain just past the toilet bend, with the Tee facing straight up vertically, as in 12 O'Clock position, so no water flow interference is possible.

as an aside, pvc prefab traps are available for the shower & floor drains, with clean-outs, and will eliminate the foul smells typically emanating from Thai house showers & floor drains.