Cleaning used sink inside overflow cavity. necessary before install?

[Gramps]

I bought a sink from the Habitat restore, and am cleaning it up before installation. It is a toto sink
I noticed that inside the overflow cavity, alot of dirty grimy gunk has accumulated.

My only concern is of sinks and odors. I don't like stinky sinks.
Is there a way to clean this.

I was thinking about blocking off the bottom of the sink and putting some sort of cleaner inside to let it soak for a few hours.
what would you recommend? what type of cleaner, or am i wasting my time

 

[Reach4]

I would be thinking about 33% bleach and 67% water. Maybe add some dish detergent too.