I got a 31 year old 5-rm, pt blk. Reno now in progress. After changing "cast iron" pipe to pvc ones, found 2 previous pvc pipes seem to be "dummy" or "redundart". One in Kitchen, one in master tiolet. Got "openings" at bootom of pipes. Found no connected to anywhere. ID & contractors said these are "wind pipe". I find no info on this and wrote to hdb yet to reply. Call them, technical guy yet to return call.

My concerns: what are these pipes for? Can I remove them.

Those are called "Vent Stack", and is necessary. It is also the souce of all the odd smells.

When the holy water flows from that magic seat into the downpipe, the air in the downpipe is displaced. The air must go somewhere. The Vent Stack is where the air is channeled to the top of the building and the wind will bring it to your neighbouring block.

If there is no vent stack, when the holy water flows down, the back pressure will cause a bubble to surface into your magic seat, along will all the natural aromas.

http://en.wikipedia.org/wiki/Plumbing_drainage_venting

Many thank for the info.

These pipes viewed externally, not connected to anyway. The openings is "2-way throght". Any 1-way valve installed?

Wondering how they are linked to the sanitary pipes?