I have a clog in my main drain that I believe started after I added (apprently too much at one time) CYA to a skimmer. My skimmer has two holes with one going to the main drain and the other going directly to the pump. My main drains also have a direct line to the pump and are on a common line with my vacuum port. I have attempted to use a drain jet from the pump forcing water back to the main drain, but my vacuum port vents the pressurized water. Is there a way to effectively stop this from happening short of capping off the vacuum port? Also, have others ever experienced this situation? Can adding too much dry chemical clog a suction side line?