Yep. Sounds like the vent is plugged or the drain line is full. On mine I can only empty the sink a couple of times before the line fills up. I don't believe there is a tank, it's just whatever goes into the drain line.
2013 Ram Longhorn 3500 Crew Cab 6.7 Turbo Diesel, Aisin Transmission.
2014 Jayco Eagle Premier 351 RSTS, Mor/Ryde Suspension and Pin Box, 17.5" wheel upgrade, 18k Pull Rite hitch.