Northstar1

2 hours ago, OneMoreFarang said:

Thanks for your answer.

About the drainage pipe. I see two problems with that approach.

 

In my condominium, and I guess in many others, some of my drainage pipes go from my condo through the concrete floor to the ceiling of the unit below me. Or to be more precise, they are hidden under the (tile) ceiling of the unit below. And in my case that unit is currently empty. The building manager agreed to help us and open the condominium below to look. And maybe we can remove a ceiling tile or two or three. But I guess there won't be a big inspection happening in the other person's condo.

 

Some leaks could be just small leaks. Just a few drops, but maybe steady. If we poor water down the drains we won't easily see if maybe 1% of that water is leaking slowly through the pipes or connection of the pipes. And if nobody is watching for some time in the condo below that might cause some bad damage...

Yes, that’s the problem with condos, at least you have an empty unit below and are able to inspect and do your do diligence. Capping filling testing etc will be the most you can do, 

remember drainage will (should) only be 1/4 to 1/3 full during everyday use, no pressure, unless clogged. 
drainage pipe generally is the least of your worries in regards to leaks if installed correctly 

wTer pipe is always under pressure and is more likely to leak over time.

correct grade on drainage is important as to carry waste , solids , and not leave anything in the pipe after use

I’m a plumber, testing piping is simple, he should have the pipes connected to the fixture and it should be valved coming

out the wall before the fixture.

EVERY fixture should have a shut off valve so you don’t need to shut the whole house down when trouble arises.

simply turn the water on before the walls are enclosed and visible. Making sure off course all valves are off. I’m certain any plumber would do this to avoid floods. But it is Thailand ????

Ask the project manager to make sure pressure piping has been tested 

drainage pipe is simply capped, filled and visual checked.

no pressure will be present in drainage with every day use!

good luck! Nice to see you got a warranty ????