underground plumbing would be the plumbing under the concrete in the basement for a future bathroom. the location is up to the homeowner but sometimes has to work around the the location of sump pump, gas meter, electrical panel, ejector pit, water meter, and sanitary sewer. if you have this feature you will need to specify your preferred position via phone call. you will also need to specify if you want it plumbed for a tub/shower unit OR shower unit. You can make that selection below.