Cleanout cap doesn't seem to go back on

[jeffoire]

Hi, I was doing laundry at my dad's house today, and the stench in the basement was intermittently, absolutely nauseating. Another site recommended to check the cleanout plug, and sure enough, when I lifted the grate, all I see is an open hole. Not too far away on the floor, I noticed a threaded metal cap that seems to be the right size, but I can't seem to get it to actually screw into the cleanout hole. Not sure it's too corroded or what (it has a very green patina). I'm wondering what I should do - is it worth trying to clean it up? Do I want to put teflon tape on it? Or do I need some kind of lubricant? (that piece of duct tape in the photo has since been removed)

 

[Terry]

Are you sure that wasn't a floor drain that dried out?

 

[Sponsor]

 

[jeffoire]

I don't think it's gone dry. The photo doesn't show it very well, but I can see water in both holes. My dad wants to pour some grease and hair remover down it, but I don't think that's going to help the smell at all :-/

 

[Terry]

I would pour water down it first and then check.
If that's a p-trap below the floor, the water will be the seal that prevents gas from coming up.

If there is no trap there, then I doubt there "should" be any standing water. Then it would need to be covered. But if there was a grate there, then that sounds like a drain.