Beneth the Kitchen sink smell

Under my kitchen sink there is a steel box (about 10 inches in length) with a pipe running into it as well as one out. To what these are connected to I do not know. I opened the box and it seemed like it was a mini settlement tank but it stinks, even when it is closed! Anybody know what it is? Or how I can get rid of this smell?

Haven't got the foggiest idea, but if it you want to get rid of the stink try going down to the pub, if you can't smell it there.....stay there

r u in america.sounds like a grease trap but iv never seen on in a domestic installation in the uk. \not to say there arnt any i cant be every where all the time. disovle some soda crystals in hot water block the pipe out side fill as much as u can & leave over night. SODA CRYSTALS . NOT NOT NOT CAUSTIC SODA.