Fresh Water Capacity (gals) includes water heater 23
Gray Waste Water Capacity (gals) with optional shower/bath 11
Black Waste Water Capacity (gals) with optional shower/bath 5
This is from Jayco's website, so you do have a gray water tank. Since it list the tank only if you have the optional shower/bath I would say it is only for the shower water. You might be able to run a drain line from the sink to the gray water tank, but the sink is on the other end and other side of the trailer. If you follow the drain line from the sink to where it exits the trailer you will know for sure if the sink is connected to the tank.