On first glance this little stopper doesn't seem like it will do the job. It doesn't automatically "suction" into the sink like I thought it would.
But, when you fill the sink it holds firm. That's the beauty of this stopper...OXO built a well executed simple kitchen helper. 
When you turn the knob, water flows right out.
I clean sinks full of fruit and veggies in large batches and this will help HUGELY! Love it.