I assure you I am not pumping out all 20 at work. I am estimating that over a 24 hour period that includes night nursing.
When I work I work such long days that I am pumping from 5 am to 9pm..
and occasionally i just get a little out.

midnight-nurse 2 oz?
4am-nurse 2-4 oz?
5am-pump 3-4 oz
645am- pump another oz or so (pumping again here is right before I clock in)
9-10am- pump somewhere between 1-4 oz
3pm-pump somewhere between 1-3 oz
7pm-pump 5-6 oz
9pm-nurse both sides
10:30pm-nurse both sides

I am still pumping this often while at work because he nurses this often at home