55 gallon drum:
First you need a plastic 55 gallon drum, dirt that can be dug deep enough to bury it, either on its side or upright, and at least 18" below frost line, poke it full of 1/2" holes, then fill it full of #57 or larger gravel. Route your drain into it. Limit the amount of solids that go down the drain to keep from plugging the gravel. The water will simply soak into the soil.
50 4" Drain line
Dig a ditch 18" deep x 12" wide x 50' long. Put 4" of #57 gravel in the bottom, lay the perforated pipe on top of that. Route your drain into the end of the pipe then seal the other end with a cap. Cover the pipe to within 4" of the soil surface with gravel. Cover gravel with landscape fabric to keep fine dirt out of gravel then fill to top with soil and sow grass on it.
Neither of these are my ideas. I think I got both of these from an old Mother Earth News magazine.