It depends on what it came from and how pure it is. Duck, bacon, beef and pork (besides bacon) is usually saved for future cooking if it is pure enough. Other and ‘contaminated’ grease is sometimes used to help start the BBQ or fireplace. Excess grease is thrown out. Very occasionally a small amount of grease will be combined with dish soap and water and poured down the drain.
We don’t often have used grease, but on the rare occasion that I fry up hamburgers/sausage on the stove, I pour the grease over other food waste and give it to the outside cats. I am sure the possums, raccons and other wildlife get some of it, too, but the cats get the lion’s share. Of course, it is always dumped as close to the creek as possible to keep our chihuahua from getting to it when he goes out to do his business (his lead doesn’t go that far) and to keep the possums, etc from getting used to coming closer to the house for scraps.
Don’t dump it down the drain. Seriously, don’t dump it down the drain even if you run hot water. I am not an environmentalist by any means, but it is a bad thing. I had to take a tour of a sewage treatment plant as part of a class I took for the Army. The plant manger told us it costs about $100 a pint to remove the grease. That is enough to get me to save an old coffee can and fill that.
SSG Schwartz
It’s not even about environmentalism - it’s about $$$$. You pay for those sewer guys to go dig grease out of the mains and manholes. Keep grease out of the sewer = lower sewer fees.
Also, if the main stops up, it may overflow in your house. Yuck.
Don’t pour it were you want something to grow. Don’t dump it down your drain. I scrap grease from hamburgers into a partially filled garbage bag. Large amounts go in a container, and get sealed before going into the garbage. Frying oil I put back into an oil bottle when cool, and toss it when it’s no longer good for frying.
Would you mind telling me more about this soap? It sounds like it’d be a good way to use up any grease I get in the future and solve the problem of birthday gifts. 
Slightly related question, then – Is using a garbage disposal bad? I don’t have one anymore, but I used to chuck most food waste down the sink disposal, and I’m sure there was some residual grease in the food.
I don’t think the little bit of grease from food down the disposal causes the problems that deliberately dumping grease down the drain does. Most of the organic matter gets filtered out at the plant and won’t be a problem. The grease attached to it would be incidental. IMO
SSG Schwartz
Sauteeing onions (and/or celery, and/or mushrooms and/or bell peppers) for potato soup, or chowder, or stuffing or whatever you saute onions and/or for.
Greasing muffin cups when making corn muffins (maybe not, if you like sweet cornbread), and to help (with butter) to start a white sauce if the sauce doesn’t need to stay white.
Frying chicken, or chicken-fried steak.
Bacon grease is good for many things. Oddly enough, or maybe not since it’s me, I don’t particularly care for bacon. So, I freeze the fried bacon for future but unknown uses.
Don’t dump it down the drain. A former neighbor had an $800 plumber bill for doing that. I don’t know the details, but the plumber (who was fixing my tree root problem) claimed he paid for his daughters weddings with grease-down-the-sink.
I rarely get any spare worth mentioning. I used to pour it down the drain, but then they changed the laws of physics so this started causing clogging, so now I soak it up with paper towels and throw those in the trash.
Go back and read post #9, the laws of physics did not change. Your grease just obeyed the laws of chemistry. At a cold enough temp, it solidified.
We let it cool and then scrape it into the garbage bag. I usually try to make sure the bag has at least some things in it before I do that, but most often it does anyway. I scrape all food residue into the garbage, so I don’t have to rinse the dishes before they go into the dishpan. All the crud gets thrown away.
Exactly, the system can handle “some” incidental grease (like off of your dishes) - more reason not to overload it with large amounts. Normal day-to-day grease amounts can still build up to create greaseballs several feet in diameter at the treatment plant.
That “hot water” argument is the one I hear most often. That’s when I point out to people that the regional plant is about 20 miles away. “Do you think your grease stays melted for 20 miles?”
Used cooking grease neatly divides into three categories:
a) Used vegetable oil (safflower, grapeseed, peanut, etc) used to fry chicken or pork chops. What to do with it: put it in the leftover fry oil container, and next time you’re frying chicken or pork chops, pour from the leftover can. Add extra from the bottle as need be, of course. Eventually discard if it gets old & rancid, gets scorched from high heat, or gets too many loose flour & etc particles in it
b) bacon grease, other forms of fresh or cured pork fat. What to do with it: put it in the leftover bacon grease can. Next time you’re cooking turnip greens, mustard greens, kale, blackeyes, butterbeans, crowder peas, or a host of other fresh vegetables, spoon in a tablespoon for flavor. If you have a goodly supply, you can use it to fry eggs in as well.
c ) beef tallow, liquid vegetable oil used to fry fish or used to fry meat or poultry that’s been dipped in batter or bread crumbs, or used to fry items liberally coated in cajun blackening spices. Umm, this isn’t reusable, pour it into an empty coffee can and when the can gets full put it in a double ziplock and discard it. Unless, I dunno, you want to use it to lubricate and waterproof your boots or something.
It’s not that great really: it creates more mess than it cleans up. Google “soap making” to see the basic process.
We made soap in AP chemistry in high school, which was about 10 years ago for me, so I don’t remember the exact process. I do remember that our soap was a vehicle for the esters we had synthesized in the previous lab (I made banana), and that the nastier the fat you started with, the better your soap.
Our chem teacher had us each bring in some fat. He said any lipid would work, so I tried to get all fancy and bring in almond oil. My soap turned out tiny and weak. The people who had brought in hamburger fat, etc. ended up with huge cakes of beautiful silky white soap. Jerks.
Potatoes fried in bacon grease are absolutely heavenly. I’ve also used bacon grease to make grilled cheese sandwiches, and these are also lovely. I am particularly fond of using bacon grease to flavor green beans.
As for regular grease, I generally pour it in a can, let it harden in the fridge, and throw it in the trash. My husband will pour it down the drain, despite all my threats and warnings.
I’ve never noticed clogging myself. All I know is that I and my parents and my parents’ parents and everyone else I knew used to pour it down the sink, and then all of a sudden (about ten years ago, at a rough guess) this became a Very Bad Thing to do.
I pour our grease into a coffee can, and keep it in the fridge:
A) In the winter months, I keep it until there is enough to be used to make suet cakes for the birds.
B) In the summer months, I keep it until that can is full, then I throw it into the garbage.
Apart from culinary re-use,soap making and bird feed (excluding fat from fowl),one could either convert a vehicle to use it as fuel,or donate the fats to someone already using such a vehicle.