I guess you're already in the midst of flushing...I hope you get out lots of stones with minimum discomfort!
No cons from my point of view to flushing while MCing...I've had the best results flushing at the end of an Master-Cleanse (I think the fasting beforehand made it all go smoother). My advice to you would be to drink LOTS of water tomorrow to rehydrate...I hope you drank lots today too!