There isn't enough time to pump

I've been back to work 3 weeks now and I have never fully emptied with a pump. I have 20 min break and I feel like most of the time is set up,break down and trying not to spill all over myself. I have everything ready to go but I only ever pump for 12 minutes tops and there is still milk in there. I'm producing plenty and have enough for baby but I dont know how long that will last if I never empty at work. Any tips or tricks of the trade?

Edit: I know the laws. Technically I am a salaried employee and not covered at all under federal law. I'm not asking about the law. I was asking for tips to be more efficient. For example, someone told me to set up my pump parts IN my pumping bra so I just change and pump. Cut down 5 minutes off my routine.