Basement drain

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
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Sounds like an ordinary trap which has accumulated a lot of "smelly gunk" over the years. Get yourself some strong soap and scrub it out with an ordinary toilet brush, then flush it with some very hot water.
Redo the bleach treatment again to sanitize it, and repeat whenever???

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Mat and Suzy wrote:

Yep, it has a "trap" designed to keep some water inside of it, that blocks the gasses from the sewage/septic system from backing up into the room.
It sounds like you *never* use it, (oops, jusr re-read, the basement is finished, ok) but if it has water in it that should be doing the trick. Just on the outside chance that the trap water is getting rancid or ???, it wouldn't hurt to flush it with a few gallons of cold water once or twice a year. It won't hurt anything, and should eliminate the problem.
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