Any safe and effective idea to get rid of cockroaches harboring in the sewage plumbing?

Question:From the sewage under, coming out on the drainage outlets, so annoying. Insecticides kills those out but down the drainage are usually unaffected. Closing the drainage outlets help a bit. Is there any solution? Thanks!

Answers:
call TERMINIX,WE HAD CAPENTER ANTS AND ROACHES COMING IN,I DID NOT FEEL SAFE WITH MY HUSBAND USING ALL THOSE SPRAYS,terminix started serving us april 2006,and we have had no trouble since,they have smart techs,no chemical orders,don't have to leave your house,the money is worth it