I'd like to convert another part of the house into a laundry room.
However, this room has no plumbing and sits on a slab foundation. It is on
an exterior wall however. The hardest part of this is tapping into the
sewer line since it's about 20 - 30 feet from the back of the house and who
knows how deep. I also have a PVC pipe sprinkler system that I'd have to
navigate around.

A plumber suggested creating a "gray water" drainage system in the
flowerbed behind the back of the house. The laundry water would drain
directly into this, saving a considerable cost of tapping into the sewer
line.

Are there any opinions out there regarding this kind of solution? Is there
an easy way to harvest the gray water and use it to sprinkle the lawn vs.
wasting it underground? Would that require a holding tank of some sort?