We are considering adding a half bath to our home and would like feedback.

We are on a slab so that complicates things some.

My best idea at this point is to convert the cubby area and a portion of the 3rd garage bay behind it to the bath. It would have an inswing door into the bathroom just to the left as you come in from the garage entry door and then would extend about 4 feet into the garage. The room size would end up about 39 inches by about 72 inches.

The nearest supply and drain lines are in the laundry room. We would need to route the supply lines from there to the new bathroom. To avoid tearing up for the drain line we would likely install one of the saniflow systems with the pump behind the toilet to pump over to the laundry drain line. Can this supply and drain line be ran through the attic or would it need to go through the wall?

Does this sound like a reasonable plan? Would it be worthwhile and reasonable in cost for what we are getting out of it?

Any alternative ideas based on the floorplan?