its a fabulous idea.
the water current would flush any dead fish though.
and, to clean it, perhaps they suck something through it to clean it.
like, they suck a string attached to a large cloth. when the string appears out the other side, they simply pull it and it pulls the cloth through.
thats how they clean out my dryer vents in my condo.
they disconnect my dryer from the exhaust pipe. they place a long string into the pipe that is attached to a "cloth". outside, they use a vacuum to make the string appear, then they hand-pull the string, pulling the "cloth" through the pipework. when it appears, its full of lint.
probably the same idea, and easy to do.