When I can't find my plug (which is most of the time) I use and old grip, slides right over the silencer (pro circut). I turn it around for Tigger's 65.
A rubber stopper from a hobby store, I had one from my home wine making and it had a hole in the middle so I put a bolt in the hole. The bolt makes it easy to pull out.
Gomer "introduced" himself to wardy at DW '00, by putting a hidden plug in wardy's AF 500, wardy kicked and kicked and then blew that plug all the way across the pits. Good stuff.