Hey Glenn, Barb
I dont usually look down this far on the forum. I check whats going on with the AA's and I'm out. I'll try to glance this way more often.
The only time my cassette or chain get removed is when they wear out. I ride between four to five thousand miles a year and this is what I do to clean the Drivetrain.
I buy Finish Line, EcoTech 2, Multi Gegreaser (Brands or any Bike shop). Spreay the cassette, derailer and two geared wheels back their, the chain and the the two chain rings on the crank. Spray them heavy. I then take the same park Brush you have and brush everything you sprayed. Now this is important: You must hose off the drivetrain( everything you sprayed with degreaser) with water.
Use a water hose and adjust nozzole to a medium mist. and rinse off all the degreaser and grease off the drivetrain. Do not use a hard stream of water. Use a Medium mist. Drivechain should look like new at this point. Take a dry rag and dry the chain, hold it with rag and spin crank. Should have very little transfer of dirt. You should be able to eat off it. Spin rear wheel to get excess water off cassett. Dry Derailer and everything back their with rag. I like terry towels. Dry chainrings on crank. Let bike sit and dry for half a hour and then lube.
Make sure you lube all the piviting areas on derailer, and lube the two wheels on derailer, and chain. Im goung to say you know how to lube a drivetrain. So I wont go into detail.
How often: Depends on how much you ride... For me I degrease the drive train once a month and always keep the chain lubed as needed. Remember I ride all year round when possible. Now if I have a riding event like the Gran Fondo on May 20 or Tour The Hamptons or am riding a century I will degrease the drivtrain before the event.
Good luck Glenn.