It continually drains, water continually comes in at one end and out the other. Sorry about the lack of pictures, I don't have any better ones on my phone at the moment or I'd take close ups.
Where I put the black arrow is where water comes in.
You can see that the water all travels unground in a pipe, and lets out into the pond.
When I get home, I can get better pictures that will explain a little better than words!
