You mentioned 'new' owners. It would be helpful to know the exact model of your camper so we can look at the plumbing setup. You can add that information to the signature line of your profile.
As new owners, it could be an operational type issue. If you have plumbing fixtures on opposite ends of your camper, you probably have two grey tanks, and are missing draining one. Get down on all fours and look for another waste valve handle, not necessarily in the same area as the others.
Are there other fixtures that use water near the sink in question? If so, do those drain correctly?
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Doug and Patience and Shelby the mutt
2015 Crossroads Sunset Trail Reserve ST26RB
2013 Ford F-150 3.5 EcoBoost XLT Supercab 4x4
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