I know this ain't the right way, BUT

I only get around to it every 3 or 4 years.
Not hard as long as you can get the plugs loose.
It may take one of those impact scrwedrivers you hit with a hammer
if they're really stubborn.

Those little pump bottle kits they sell at wally world make getting the new
stuff in a lot easier. You screw it into the bottom hole and pump till it flows
out the top hole. Then put top plug back in before you unhook the bottom
and plug it.