For the rubber plugs, here's what I did. The rubber plugs are thin walled. If you use much force pushing them in, the end will punch out. After I ruined a few of them, I took some small thread from a piece of paracord (internal part of the paracord) and tied it to the nipple end of the plug and pulled it thru the firewall with no more breakage. Others have had success using screws threaded in them and pushing. Also using different objects to push them in. I tried without success until I used the strong paracord string to pull them thru.