The cassette isnt too bad. Fill top fresh with fresh water only. Take the black tank out, add 4oz of chem and about 2 liters of water via the black tank dump spout. You're set to 'go'.
Empty before leaving the CG and rinse thoroughly when you arrive home. I fill about 1/4 with water to the dump neck of the black tank, shake a bit then dump about 2 or 3 times.
Winterize by the same plus remove the top of the black tank and (with rubber gloves on) rub olive oil on the tank seal before winter storage. 3 years in and I'm still good. Same Thetford model the 124 has in my a126.
2011 FR Rockwood Premiere A126 Hard Side
TV=2011 Jeep Wrangler Sahara 2 Dr
Reese 66065 WDH, Curt WDH Shank #17120
Prodigy P2 Brake Controller, Mopar 7-pin Harness
B&M Transmission Cooler (#70268)