On Jul 25, 4:36*pm, "MiamiCuse" wrote:

snip

Third link shows clean out on the left with letters 'C.O.'.If that is
original marking it could mean "clean out", so concentrating on that
one seems best place to start. A diamond hole saw from Harbor Freight
would be a low cost way to get through the concrete with little danger
of drilling into something vital.

Joe