I am relocating washer and dryer in a garage that was remodeled by the original owners to have two bedrooms and a craft room. This remodel is very dated and disjointed and we are wanting to add a bathroom in this very large craft room, but it is on the other side of the house from the main bathrooms and the rest of the home was JUST refloored. Very near the remodeled area though is the outdoor clean out that then connects to the main house. It is close enough the cleanout couldn’t be more than a foot top to bottom below the surface. As I am unsure where the waste lines are located I feel it would be more reasonable to tie in between the clean out and the rest of the plumbing (just outside of the house) and have a separate vent stack for the bathroom addition and washer.
We currently have a concrete slab throughout and an ugly linoleum in the area for the bathroom addition. The closest drain I could tie into otherwise is a kitchen sink which would likely be undersized for my overall purposes.
Any reason why I shouldn’t proceed with the addition this way?
I’ve attached an image of the layout with approximations if he plumbing. I would rather not destroy expensive brand new floor if I could instead go through the linoleum located in the garage area and two adjoining bedrooms. 
Best Answer
Allow me to recommend you call a licensed and reputable plumber to come and look at your house and make recommendations. Surely you can find someone who for $150.00 will come and tell you what you can do. You could go the sly route and request a quote, you could offer to pay for it, and then ask a lot of questions. Make sure to ask for and get, with your quote a simple drawing and piping lay out. Good Luck.