I know this will come in bits and pieces because I'm kind of slow when it comes to prepping for making soap. I save grease/dripping in canning jars and then store them in bread bags in the freezer. When the time comes I thaw them to clean out the particles such as bits of meat.
Depending on the soap I am making it can take up to 5 pounds of grease. I have two partially filled cans of shortening that has gone stale so I have plenty but I still wanted to use the drippings first.
I should explain that each solid fat has their own property when it comes to soap making. The softer your fat is at room temperature, the softer your soap will be. That is why it is never recommended to make soap with just liquid fat (oil). Drippings are often firm enough to make a good solid soap but we don't cook enough fatty meats to get enough for a batch of soap. These two jars have taken us nearly 2 years to collect.
Cleaning drippings is easy but it takes a lot of time (mostly waiting). I made the mistake of starting with a pan that was too large. I had expected there to be more fat than there was.
Fill your pot with hot water out of the tap.
Add the grease.
Heat the pot on the stove until the grease is all melted. Do not let it come to a boil because the foam will cause the particles to sit on the top of the fat.
When the grease is melted, put the pot in your fridge overnight. I put mine outside since it's really cold right now with a towel over the top to prevent stuff falling into the pot.
Now you will see that I had particles float to the top. I left the pot on the stove for just a little too long.
If you use the right sized pan, you can remove the fat, sometimes in pieces and scrape the top and bottom to reveal a fairly clean piece of fat. In my case, my piece came out rather thin. You may have to repeat this process several times to get the grease as clean as possible. Knowing this, I cleaned what I could off the bottom of the fat and placed it all in a smaller pot.
The cleanliness of the oil will depend on where you get your drippings. We keep a jar by the stove (in the really hot season we put it in the fridge to prevent it from smelling). You can use rancid grease. It doesn't make pretty soap but it's still usable soap. We save oil that we deep fried with (straining it before pouring into a canning jar). We use oil that has gone stale.
Soon, I'll post the instructions for turning that grease into soap. I have posted a laundry soap recipe previously.