Hold on there... A 3-inch drain just for a washer? Why so huge? Half
that size is typical.

Also, a block wall is only 6" thick. A 3" pipe buried inside would
require a 4" deep cut, at least, which would pretty much destroy the
integrity of the entire wall. And that wall could easily be load
bearing, too.

I'd just route a 1-1/2" pipe using your "inside" idea. Your washer hose
might not fit in the pipe, in which case just add a 2" diameter stub on
the end, with a reducer fitting.