Smell from Drain in conservitory

[ultrasonix]

ok we built a conservitory on the back of the house its 1930s building and all the drains appart from toilet go into outside open drains this was the case when we bought the house and its really not been an issue how ever recently theres now a smell from the Drain thats in the conservitory i took up the metal cover we fitted and checked the drain the water isnt clear in there even if i run clear water for a long time from the sink in the kitchen which drains into this drain. can i seal the top as i have u traps on all the appliacnes and the sink the only smell is from the metal covered open drain and what problems could i cause

ive put all sorts of cleaners and rods down the drain and lifted the man hole covers on my drive all free flowing no back logs.

any help with this before i kill the wife for complaining about the smell.

 

[freddiemercurystwin]

Is this a gully or a manhole in the conservatory? If a gully, are you seriously asking why the conservatory smells if its a gully connected to the sewers? If its a manhole it should be the sealed type that does not permit smells.