It handles rainwater coming off the barn roof, that's it. Actually, it's off half the barn roof, no effluent. It's uphill and 100m away from the house.
As far as I can tell, there is one inlet, which is right at the top and easy to access at the other end. The top of the silt is about 7' down but don't know how deep it goes. I'll try poking something a little more rigid down there to see.
There are no outlets, at least, not that I can see (and I've drained it down to about 4" of water, when the pump float falls). The drain I'm pumping it into is about 2' down below the top of the soakaway