House is 11yrs old. 3 toilets/2 up-1dn. 6mo ago (+-) they ALL started clogging randomly. Not all the time & not the same one. No telling which one it will be. Had plumbers check vent stack/ works fine,strong air flow. Cesspool pumped & working properly. When clogged, I use a Rigid closet auger(6') to get toilet flowing again. Regular plunger wont do it. Even took downstairs toilet out to check wax ring,etc. All good. reinstalled toilet.All working now. Just waiting for the next clog! Help!