what up bro. thats not the only way to get a good bead though.
what size is that sub? chances are that you arent going to be able to clean that off properly.
if it were me, i'd be pissed at that recone job
then i'd look @ the spiders to make sure the glue isnt all white and brittle.
then after that i'd order a full concave dustcap for a 15" sub.
cut that BS off of there thats on there now, and make sure nothing is loose or flaking off, then lay the larger dustcap over it, glue it down with some Goop or something similar, and let weight sit on it for about a day
then bang out.
-Robin