Looking at the instructions

I have with the overflow kit 2 inserts included are these to be used when using flex hose or ridgit pvc pipe or should I get adaptors? (they are 1 inch outflow and 3/4 inch for the return and go right under the bulkhead and looks like its the only pieces in the whole overflow parts list that require pvc glue
just courious (it an oceanic overflow kit)