How to reduce milk supply

I am returning to work soon and like to reduce my milk supply gradually. I have been increasing my pumping interval from 3 to 4 to 5 hrs (each 20mins/breast) for the last 5 days. My breasts is starting to clog and I worried it will cause mastitis. Can I take lechthin to remove these clog? How to reduce milk without getting clog and mastitis?