Couple of observations from a 30+ year Patterson tank user. Always start vigorous agitation as soon as the developer is poured in. Most developers froth as you pour them in and you have to get agitation started straight away. I do about 4 inversions in a 10 second period where the tank is turned completely upside down, hold the tank upside down for a second or two to make sure all the developer drains off the film and then turn the tank back right side up. Always tap the tank sharply on the counter after agitation and make sure to "burp" the lid after the solutions are poured in. I never used the twirler as I usually lost them soon after buying a new tank and I don't believe they give enough agitation. If you have ever seen a nitrogen burst developing setup you will never be afraid to give a film too much agitation. I do all my film developing on a jobo now which is continuos agitation.