Mike, my description isn't real good. But the problem is, the stopper is either all in, sink fills up, or all out, big drain hole to lose stuff, and you have to physically take the stopper out so it drains. Every RV sink I have seen you could pull the stopper up, give it a quarter turn and it drained yet stayed in the sink, and prevented things from going down the drain.
Camper_bob, thank you for the idea. It will give me something to work on.
I thought maybe my sink is defective, or the stopper. But I haven't found anything to replace it with. I figured a home remedy was at task!