[whatsnewell]

Unfortunately, Glenn's setup (courtesy of the prior owners) does not allow the gray water to enter the holding tank anywhere but at the bottom where you would normally open the valve to dump the tank. If that valve were open when the other valve is closed the gray water could enter the tank, but at some point the gray water would stop being admitted to the holding tank when the water level gets to a certain point. Ideally there should be some place, such as the vent tube mentioned by Kyleb, for the gray water to enter somewhere up higher.