We have the water run to the front of our washrack, into a sort of trough with tile in it, then it runs downhill and out the end of the tile about 50 feet away from the barn. The trough with the tile keeps the tile underground from getting clogged. We just have to clean the straw and poop out of it every week or so. Not the BEST system, but the washrack took very little work to put in place..and it has worked for us..
We have it cemented with a regular grate at the bottom of it, its sloped some, but they are struggling with the drainage part out side, they are piping it underground and under the
barn to the outside,they dug a deep big pit and put a huge barrel in there but dont know what to do next
ours has an 8 " drain with cover the cememt is slanted around the drain. our out flow goes under the cement and hooks to a tile outside that hooks into a drainage tile that goes thru one of our lots. We have had this for a couple years and it works really well.
I just ran my drain pipe under ground to a hill side. A friend of mine talked to someone that has built several that have worked very well. This is a different method, they barry a large car body in the hole and fill the car body full of gravel. The car body keeps the hole from completely settling and packing. The drain pipe is ran into the hole and carbody.
Our washrack drain sound like the way you built yours. We have 6 gutter drains that come off of the barn and they are all connected with piping underground to the wash rack drain (that way when it rains it cleans out the wash drain) the main pipe then daylights out in the field. Our excess water runs downhill into the pond where (when we are finished) the water will be run through a filter system and then be pumped back into the barn water line for reuse.