Cast iron skillets can usually be cleaned with just a quick wiping out with paper towels or a nylon scrubber. Hot water will handle the next escalation. Dry the pan by heating it afterwards, then a wipe with oil on a paper towel.
You don't need to oil it every time. You don't even need to oil it after cleaning and drying, unless you're not planning on using it for several weeks (or you live in a very humid environment).
Within an hour or two of cooking, I wash my cast iron pans with gentle dish soap, then dry them and put them on the burner, lowest flame, for 5 minutes to ensure they are fully dry.
You're absolutely right that moisture is one of the biggest enemies of cast iron. Even a small amount of moisture left on the surface of the skillet can cause rust to form over time. It's important to dry your skillet thoroughly after each use, especially if you're going to be storing it for any length of time.
Cooking with a cast iron pan that has a little bit of surface rust on it isn't likely to hurt you. If your pan is seriously rusty or has visible rust flakes, you shouldn't cook with it until the rust is removed and the pan is washed and re-seasoned.
Black Residue
There can be residue from the seasoning that may come off your seasoned cookware. The residue is not harmful in any way and will decrease as the cookware is used over time.
Wash your cast iron cookware by hand. You can use a small amount of soap. If needed, use a pan scraper for stuck on food. For stubborn, stuck-on food, simmer a little water for 3-5 minutes, then use the scraper after the pan has cooled.
Common cooking oils like olive oil will gradually produce seasoning, but won't be as effective as grapeseed oil. Canola, other vegetable oils, and shortening are a little better.
Cleaning by hand in soapy water is enough. The pan must be cleaned each time it's used to remove the film of grease that can stay on the surface.
Most cast iron skillets these days come pre-seasoned, meaning they're ready for cooking on as soon as you take them out of the box. However, over time, the seasoning erodes, and you'll need to re-apply it by brushing the skillet with a thin layer of neutral oil and heating it until the oil bonds to the metal.
In general, your pots and pans should stay away from the dishwasher. Non-stick, cast iron, and aluminum pots and pans should never go into the dishwasher. Non-stick coating will wear out in the dishwasher, cast iron will rust and lose its seasoning, and aluminum will be covered in nicks and scratches.
It's important to not use anything too aggressive such as steel wool, sponges or other abrasive cleaning methods as these will strip your seasoning.
Doing so can cause the all-important seasoning on the surface of the pan to flake off. This not only results in unappetizing black flakes in your meal but also degrades and chips away at the seasoning, which is paramount when cooking with cast iron.
Oil, especially canola oil (bad, unhealthy oil), should not be used. If a quick oiling (not seasoning) in between is desired, it's best to use a high temperature oil like avocado. A quick rub can do the trick, if your pan looks a bit dry. I have one pan that is about 100 years old!
Bake your cookware upside down at 450 degrees Fahrenheit in the oven for one hour. Allow the pan to cool down completely, and repeat three more times.
Best High Smoke Point Oils
Refined Avocado Oil - The smoke point of refined avocado oil is between 480 to 520 degrees Fahrenheit. Canola Oil - All canola oil is refined and has a smoke point between 400 and 475 degrees Fahrenheit. Grapeseed Oil - Grapeseed oil has a high smoke point of 420 degrees Fahrenheit.
You let your skillet soak.
Soaking your cast iron skillet in your sink is a recipe for rust, as is washing it in the dishwasher. Instead, clean it ASAP, even using simple soap and water if you must.
Clean your cast-iron skillet each time you use it. Doing so prevents stuck-on food from staying on the skillet between uses. If the skillet is only slightly dirty, a quick wipe after cooking in it will work. If dirtier, or food is stuck, then scrubbing it is best.
For a small amount of rust, just scour it with a scrubber and water like normal and rub with oil. But if you've got a bigger problem, luckily, a little white vinegar and elbow grease are usually enough to whip that pan back into shape.
Cooks for generations didn't use soap on cast iron pans because the soaps were made with lye and vinegar, two ingredients that will absolutely strip the seasoning and can even damage the pan's iron. Today's aerosol oven cleaners are often made with lye or sodium hydroxide.
Since olive oil is such a pantry staple, many people naturally wonder if they can use olive oil to season cast iron. You can use olive oil to season cast iron, but you need to choose a high quality extra virgin olive oil, which should have a smoke point close to 400 degrees Fahrenheit.
The most common reason food sticks to cast iron is because the pan is simply too hot. Because cast iron retains heat much better than other types of cookware, you generally don't need to use as high of a heat setting as you normally would with stainless steel or aluminum cookware.