Rearly bad sewerage smell

[charlie2009]

I have an apartment in portugal.The block is on 4 floors with 8 apartments.Over the last couple of months there has been a rearly strong sewerage smell in all the apartments and stairwell.It comes ad goes lasting upto to 6/10 hours each time.Sometimes you have to go out its that bad.i have had the manhole cover up and its not blocked or backing up into the apartments.Anyone have any ideas what could be causing the problem.

 

[leadpig]

build up of gas in the sewer

 

[charlie2009]

What can be done about it?

 

[Plouasne]

What can be done about it?

Vent the soil stack or drain to fresh air, minimum hight of open terminal 1 mtr above the top most open window or 3 mtrs in a horizontal direction