Do not clean the walls unless some parts have food or grease on them.. That is the seasoning, you need it!! I pitis mucked up in the bottom grub it all out. If it is cooked on put some hot water in the pan and set temperature to about 275 and let it steam. should soften everything, then clean the bottom and the grates.
When it is clean line the bottom of the floor with aluminum foil. Punch a hole in it where the grease drips through. Cover the tops of the other parts that might get dripped on. Do your cooking then just take them off and dispose. Clean up any small amount that might remain in the bottom, clean the grates. Put about half cup of water in water pan, heat the unit up to around 275 deg. for about 45 minutes. The steam will sanitize the inside. Open the door, empty the water pan if any remains, leave the heat on, close the door, let it heat up again, open the door, let steam out , close door open vent completely and it will dry it self out. Sanitized and ready for next smoking. Cover the pertinent parts with foil again and your ready again.
Learned all this reading other threads..