I have to install a dryer outlet in a garage where it has unfinished
sheetrock. I purchased a surface mount outlet similiar to this one:
http://www.acehardwareoutlet.com/(x1...aspx?SKU=33287

It came with 2 half moon clamps for the wire, and the instructions say
for wall mounting, put the clamp on the bottom knockout. For floor
mounting, use the knockout on the back.

This would mean that I would have to come out of the sheetrock with
the wire, then turn up 90 deg to the outlet. Is this right? Is there
any reason why i cant use the rear knockout so I can come inside the
sheetrock and through the rear knockout?