At some point in the past

someone added a toilet, big fiberglass utility sink, and the washer\dryer hookups in my garage. They busted out the whole section of concrete and put all the necessary pipes in and then re-poured that whole area.
It is walled off into a room. The only way you can tell..is under the door itself...you can see the crack and a very very very slight change in the color of the concrete.
I love it! Working in the garage I have a half bath and do not have to track through the house. The big sink is great for washing up and some parts washing.
I am sure others will chime in on the how to side, but it is well worth it IMHO.