Downloading And Installing All Updates At Once

I have now taken over the formatting of laptops at my work place. We buy and sell second hand laptops, so want to erase all data before we sell them. Everything is fine, but the updates take forever, and need you to be around to continually restart the computer numerous times. I downloaded WUD and downloaded every update at once, but still found that they could not all be installed at once (Unless I did something wrong), So I was wondering if there is some way you can install all the windows updates at once, as that would save me so much time, as some of the updates take forever to install, making the whole process a good 4-6 hour job sometimes.