Rapper Action Bronson -- Port-A-Potty Break During Concert ... Without Missing a Beat

Talk about having "flow" ... rapper Action Bronson TOOK A PISS in a port-a-potty during a live concert this weekend -- while continuing to RAP during the ENTIRE bathroom break!!!

Bronson was performing his song "Shiraz" at the Ottawa Bluesfest on Saturday when nature called -- but he didn't stop the show ... he grabbed the mic and continued to rap while he strolled to a bank of blue toilets.

Then ... while in the pisser ... he CONTINUED TO RAP -- without missing a beat!!!

He eventually emerged to huge applause ... and continued to rap as if it were no big deal. .

The most impressive part -- it looks like he used a paper towel to open the door from the inside so he didn't have to touch the handle ... WHILE RAPPING!!!