Just out of curiosity,how do you know the slope of the drain is "miscalculated?" For example, could it be undersized pipe of correct slope? OR???

The term you want is 'backflow preventer' (but I am also seeing 'backflow valve' and 'backwater valve' so take your pick). I have seen them put on a sewer lateral (between house and sewer main) to prevent backflow into the house. They are also made for water supply lines so a search for them will often result in many hits for brass ones designed for water lines.

I should think, if you have flooding from drain backflow that has nothing to do with you but is coming in from the main drain, the bldg owner should take care of it. {Edit: I see upon rereading that you have a condo, not an apt., so you own probably everything on your side of the connection to the main drain. So entirely possible you may have to pay for a backflow preventer yourself. But doesn't hurt to ask.]

Here's a 2" one so they are available in the size range you would need.

https://www.amazon.com/American-Valve-P32S-Socket-Schedule/dp/B000LF61DY/ref=asc_df_B000LF61DY/?tag=hyprod-20&linkCode=df0&hvadid=193984242218&hvpos=1o2&hvnetw=g&hvrand=15924540748615189069&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1020268&hvtargid=pla-338104952154&psc=1

I do not think it is possible to comment “is it possible” without a site visit.

Re responsibility, need bry for that.

lol

Hi all,

Here are further details.

To

SaltiDawg: sure it could be both but still something wrong with the building design anyway.

DavidR: The drain in not linked to my washing machine.

it is a hole in the floor in case the washing machine overflows.

toxcrusadr: Thank you very much for your suggestion and advice.

Jim Mat: to clarify my question:

Is it possible to install something to prevent backwater in a drain afterwards - while the wastewater line is in use.

I have seen drain mechanisms for other applications that have a float in them (it looks like a ping pong ball), and if water backs up the wrong direction it will float the ball up and plug off the drain. However, I've never seen one for standard plumbing applications.

Bruce

But maybe not the slope of the drain line... as you said, you don't know... yet you stated "with a miscalculated slope, so it's prone to clog." lol