This is a hard one. 2014 Rushmore Lincoln. I have figured out that the bottom gray tank drain handle matches with gray tank #2, but I do not know if that is shower/bathroom sink (I'm guessing they drain together) or the kitchen sink. Anyway, I pull the handle to drain, the handle pulls out like it seems it should (similar to the other two), but hardly any water drains out. I will have to leave it open for a few days to get it empty.
I have glanced at the bottom of the RV, that is some serious sealing. It looks and feels like a thick plastic board, solid, and mounted on either side by a long aluminum strip and screws. Even where the drain tubes come through, they are sealed with some type of black firm sealant. I do know that I can get into the crawl space where the backside of the drain cables are (along with water filter, water heater, furnace and such) but I haven't done so yet.
What I don't know: perhaps the cable needs a major adjustment? is there an access panel on top to get to the valves? if this is the kitchen sink drain, did the previous owner dump hot grease down the drain and it solidified at the valve? I am really at a lose on what to even try! Suggestions?