Many people with larger yurts choose to frame out an interior bathroom rather than attaching an exterior bathhouse. This could be done (after the yurt is installed) in much the same manner as in a conventional site-built structure and is typically done by a local carpenter or contractor. The plumbing would be brought up through the floor of the yurt into the bathroom. Venting from the bathroom can be accomplished with downdraft vents through the floor or through the wall of the yurt using a flashing kit. Proper ventilation will reduce moisture inside the yurt and prevent condensation.
Looking for inspiration on designing a bathroom in your yurt? A PDF copy of our Bathroom Ideas Flyer can be downloaded here.