The wash is right at the point where the ocean ends and the beach begins
It's a depression that's only about 2 or 3 feet wide.
Further out from the wash there's higher "shelf" before the drop off begins This drop off between the shelf and the bars is called the slough.
The massive volume of water that comes over the bars causes the longshore current to set up in the slough.
This water needs a place to escape and that's the rip current
The wash is just a depression caused by the receding waves flowing back off the beach.
The currents are caused by the volume of water in the waves needing a place to level out
Here's good picture of a rip current.
The wash is at the base of it