If you are living street level, it is possibly effluent from other houses trickling down the street.????????

11 minutes ago, hotchilli said:

Agreed, masking it with concoctions is of no use, it will return.

Install a proper P-trap or "U" bend water trap.

Solution is final...

 

There is nothing improper about a bell trap and it will work fine with water and can be easily cleaned from floor level without the need for chemicals. 

21 hours ago, Mickeymaus said:

If you use a cover then something that floats on water. I put there a plastic bag filled with water. Was pretty airtight. But then a water hose broke in this bathroom and the water could not run down the drain. I have learnt my lesson ????

Agreed. A dodgy water-hose (bum gun) can cause a lot of damage in a short time.????????

 

23 hours ago, Maybole said:

What is a "P" trap?

https://images.app.goo.gl/1rRqH5QHWfYcLXmk8

 

The J bend in the pipe holds water so sewer smells cannot backflow into home

Edited December 10, 20223 yr by mania

These qucik fixes may not work if it is a building construction issue.

First off I would ask other tenants in the building if they are having the same problem. If so it could be out side veneration problem