How do I deal with a smelly basement drain pit?

I have a nasty sewery smell emanating from the basement drain pit in my basement, after it became damp when I let my dehumidifier hose run into it (making it damp). The hose and drainage area quickly developed a nice smelly bacteria colony.

The house is from the 1950's, and this pit is part of the old foundation drain / french drain / weeping tile. The bottom of the pit is dirt/clay. I tried digging down about a foot into the dirt and didn't find any hard bottom.

I can't really clean it out properly since it's dirt. And it's not obvious where any water would actually drain to, if I were to try rinsing it out with a hose.

Clearly it needs to be dealt with (because it's smelling up the house) but I'm pretty stumped what to do with it....