I have a split level house in Minnesota with a finished basement. The house is about 25 years old (we moved in 6 months ago). In the basement there is a drain by one of the external walls. It is circular, with about a 6-8" diameter, and when you take the grill off, underneath there is a fairly small hole (about 2" dia) with a float of water (pretty dirty). I think this drain is the source of bad smells we have noticed recently, so yesterday I poured a few cups of bleach down there (seems to have helped somewhat).
What is this drain for, and how does it work? Presumably there is some kind of u-bend arrangement, as when you pour liquid into it, it maintains the same level. Is there anything else I could do to get rid of the smell?
TIA
Mat