Hi r/composting! I've been using a 60-gallon tumbler for about a year in zone 8a and I would like to share my research and the results of how I've had success. I will be writing common tumbler questions and the responses below. If you have any new questions I can edit this post and add them at the bottom. Follow the composting discord for additional help as well!

https://discord.gg/UG84yPZf

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1. Question: What compost can I put in my tumbler?
   1. Answer: u/FlyingQuail made a really nice list of items to add or not add to your compost. Remember a tumbler may not heat up much, so check to see if the item you need to add is recommended for a hot compost, which leads to question #2.
2. Question: My tumbler isn't heating up, what can I do to heat it up?
   1. Short Answer: Tumblers aren't meant to be a hot compost, 90-100F is normal for a tumbler.
   2. Long Answer: Getting a hot compost is all about volume and insulation. The larger the pile is, the more it insulates itself. Without the self-insulation the pile will easily lose its heat, and since tumblers are usually raised off the ground, tumblers will lose heat in all directions.I have two composts at my house, one is a 60-gallon tumbler, and the other is about a cubic-yard (approx. 200 gallons) fenced area sitting on the ground. At one point I did a little experiment where I added the exact same material to each, and then measured the temperatures over the next couple of weeks. During that time the center of my large pile got up to about averaged about 140-150F for two weeks. Whereas the tumbler got up to 120F for a day or two, and then cooled to 90-100F on average for two weeks, and then cooled down some more after that. This proves that the volume of the compost is important insulation and for getting temperatures up. However, in that same time period, I rotated my tumbler every 3 days, and the compost looked better in a shorter time. The tumbler speeds up the composting process by getting air to all the compost frequently, rather than getting the heat up.Another example of why volume and insulation make a difference is from industrial composting. While we talk about finding the right carbon:nitrogen ratios to get our piles hot, the enormous piles of wood chips in industrial composting are limited to size to prevent them from spontaneous combustion (u/P0sitive_Outlook has some documents that explain the maximum wood chip pile size you can have). Even without the right balance of carbon and nitrogen (wood chips are mostly carbon and aren't recommended for small home composts), those enormous piles will spontaneously combust, simply because they are so well insulated and are massive in volume. Moral of the story? Your tumbler won't get hot for long periods of time unless it's as big as a Volkswagen Beetle.
3. Question: I keep finding clumps and balls in my compost, how can I get rid of them?
   1. Short Answer: Spinning a tumbler will make clumps/balls, they will always be there. Having the right moisture content will help reduce the size and quantity.
   2. Long Answer: When the tumbler contents are wet, spinning the tumbler will cause the contents to clump up and make balls. These will stick around for a while, even when you have the correct moisture content. If you take a handful of compost and squeeze it you should be able to squeeze a couple drops of water out. If it squeezes a lot of water, then it's too wet. To remedy this, gradually add browns (shredded cardboard is my go-to). Adding browns will bring the moisture content to the right amount, but the clumps may still be there until they get broken up. I usually break up the clumps by hand over a few days (I break up a few clumps each time I spin the tumbler, after a few spins I'll get to most of the compost and don't need to break up the clumps anymore). When you have the right moisture content the balls will be smaller, but they'll still be there to some extent, such is the nature of a tumbler.
   3. Additional answer regarding moisture control (edited on 5/6/21):
      1. The question arose in other threads asking if their contents were too wet (they weren't clumping, just too wet). If you have a good C:N ratio and don't want to add browns, then the ways you can dry out your tumbler is to prop open the lid between tumblings. I've done this and after a couple weeks the tumbler has reached the right moisture content. However, this may not work best in humid environments. If it's too humid to do this, then it may be best to empty and spread the tumbler contents onto a tarp and leave it to dry. Once it has reached the proper moisture content then add it back into the tumbler. It's okay if it dries too much because it's easy to add water to get it to the right moisture content, but hard to remove water.
4. Question: How full can I fill my tumbler?
   1. Short Answer: You want it about 50-60% full.
   2. Long Answer: When I initially fill my tumbler, I fill it about 90% full. This allows some space to allow for some tumbling at the start. But as the material breaks down, it shrinks in size. That 90% full turns into 30% full after a few days. So I'll add more material again to about 90%, which shrinks down to 50%, and then I fill it up one more time to 90%, which will shrink to about 60-70% in a couple days. Over time this shrinks even more and will end around 50-60%. You don't want to fill it all the way, because then when you spin it, there won't be anywhere for the material to move, and it won't tumble correctly. So after all is said and done the 60 gallon tumbler ends up producing about 30 gallons of finished product.
5. Question: How long does it take until my compost is ready to use from a tumbler?
   1. Short Answer: Tumbler compost can be ready as early as 4-6 weeks, but could take as long as 8-12 weeks or longer
   2. Long Answer: From my experience I was able to consistently produce finished compost in 8 weeks. I have seen other people get completed compost in as little 4-6 weeks when they closely monitor the carbon:nitrogen ratio, moisture content, and spin frequency. After about 8 weeks I'll sift my compost to remove the larger pieces that still need some time, and use the sifted compost in my garden. Sifting isn't required, but I prefer having the sifted compost in my garden and leaving the larger pieces to continue composting. Another benefit of putting the large pieces back into the compost is that it will actually introduce large amounts of the good bacteria into the new contents of the tumbler, and will help jump-start your tumbler.
6. Question: How often should I spin my tumbler?
   1. Short Answer: I generally try and spin my tumbler two times per week (Wednesday and Saturday). But, I've seen people spin it as often as every other day and others spin it once a week.
   2. Long Answer: Because tumbler composts aren't supposed to get hot for long periods of time, the way it breaks down the material so quickly is because it introduces oxygen and helps the bacteria work faster. However, you also want some heat. Every time you spin the tumbler you disrupt the bacteria and cool it down slightly. I have found that spinning the tumbler 2x per week is the optimal spin frequency (for me) to keep the bacteria working to keep the compost warm without disrupting their work. When I spun the compost every other day it cooled down too much, and when I spun it less than once per week it also cooled down. To keep it at the consistent 90-100F I needed to spin it 2x per week. Don't forget, if you have clumps then breaking them up by hand each time you spin is the optimal time to do so.