there is a huge and somewhat heated discussion on another thread about this very subject. (can't figured out how to link the thread yet...) In short, until the 2016 model, the 313 had two grey water tanks, one dedicated to a washer which would prob never be used, and one for everything else. This was a production error apparently, and not the intended design. I almost...no...was going to cancel my purchase of this trailer on the day of the PDI because of that, and due to the discussiion on this forum, GD figured out what had happened, and redesigned the system. I waited for the new system and am glad I did. There are now (2016) three grey water tanks, one for a washer, with the t-handle in the compartment. The other two, which are also now linked, have the drain valve under the coach near the sewer pipe. The black tank drain handle is now also under the coach aft of the sewer pipe. Only the washer tank is in the compartment. Otherwise, on yours, that handle in the compartment is only for a washer if you have one. Hope this helps. You might contact GD to see if there is a refit being offered yet on pre-2016 rigs. They indicated they would be working on that.