The appropriate diameter of Penetration Seal must be used. There must be a tight fit around the pipe service or service penetration but should not be forced over the pipe or service penetration. The Penetration Seal collar extension can be trimmed to ensure the best fit to the penetration. The surface of the flexible and rigid underlay to receive the Penetration Seal must be clean and dry. When the Penetration Seal is used in a retrofit installation, the collar extension is pushed through from inside.