While we wait for the make/model, if it's a new to you rig, I'm willing to bet you have another pull handle that is hard to see/find. Check up by the frame around the tires- some of them are really stupidly placed.
2018 Ram 3500 DRW/crew cab/long bed/4x4/4.10 gears pulling a 2017 Spartan 1245 by Prime Time
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Look under the sink. You may have to remove some panels. We found our sink drain line to have a 180 degree bend in it that basically plugged the hose. Had a u shaped pvc hose inserted to take out the kink. Bad design and installation at the factory.