I know this post is old but I Thought I might be able to help .. the Head is probly a recurculating Head .. has a lever at the bottom to dump it into the holding tank ( this was a normal install in the year holiday ) when you pulled the lever it dump the waste into a holding tank under the starboard side bed. Sometimes when the tanks go bad people only use the holding cap. of the head and when they are ready to pump out the pull the lever then pump out.. Let me know if you find it ....