Foul smelling gray water under basement floor

Hi, thanks for reading! My house is fairly old, and has an unfortunate design eccentricity.

Basically, there is a grey water bed directly under the concrete floor of my basement. There are two drains that drop directly down into it, with no water trap or anything. Until recently, laundry and sink water from all three bathrooms drained down into the bed, along with run off from two of the drainage gutters on the roof.

I think at one point it used to drain out from under the basement to somewhere else in the yard, but now it will just back up if more than a small amount of water drains into it. I had a horrific flood in my basement as a result. After talking to several contractors, a friend of mine put in a sump pump that pumps the water out from under the house into the sewer line when it gets too full. We also rerouted the sinks into the sewer, and the roof drainage elsewhere.

Since then, things have been working well. No floods or back ups.

But now, a horrific odor is rising up out of the basement floor drains. I work down in the basement so much that I practically live down here, so it's really disruptive to my life. I guess maybe there's bacteria thriving down there, I'm not sure.

So, any ideas on how to clear out this stench? I've had two suggestions so far.

1.) Pour some Clorox down there.

This strikes me as a bad idea. If there is any ammonia down in that hole, the bleach will form chlorine gas and possibly kill everyone in the house.

2.) Pour some OxyClean down there.

I'm not aware of anything terrible that could happen from this. Might this be a reasonable thing to try?

I'm totally open to any other suggestions, except for the obvious "dig up the entire house and yard to fix the problem." I'm sure that will have to happen some day, but today is not that day.

Thanks!