Coffee grouns are considered a green. Do you have friends with ornamental grasses? If they prune them down now for the spring growth, this would be a good source of browns. A little sawdust, perhaps? If you are pruning shrubs, trees, in your yard and cut the pieces up small, those are browns too (but they do take a while to break down). Even if you do not have the perfect balance, you will still get compost, it may just take longer. I am in the East mountains and it is a very, very rare thing for the compost to get smelly in our very dry climate.

I used a tumbler for two years and it tended to clump up. A number of factor may cause it: 1) too much moisture 2) not turning it often enough 3) materials not shredded or reduced to small enough size I mixed the materials before putting them in the tumbler and that helped a bit. The center bar rusted thru after four years, but by then I had switched to mesh bins piles.

Plenty of info on the link below.. Here is a link that might be useful: Compost Tumbler

I shouldn't split hairs but an anaerobic pile can be hot. Or more precisely, a hot pile can run itself out of air and be hot and stinky. Just make a pile with too many fresh grass clippings and you'll see what I mean. Sort of a special case though, not suggesting a small pile or tumbler that has gone anaerobic will always be hot. Usually not, at least for very long. Just for kicks I will also include here the bizarre case of the Bridgeton Landfill in St. Louis, which has undergone a 'runaway anaerobic thermal decomposition' which the state regulators prefer to call an 'underground smoldering event' and the media likes to call a 'fire'. It is not a fire, but more like a very hot compost pile, without air. Runs about 200-300F and makes the most bizarre God-awful stink. I suspect there are some purely chemical reactions going on down there at those temperatures too. I mention it here only for the wow factor, not to suggest it has anything to do with a home compost pile. It would not really be possible for this type of thing to happen anywhere other than a landfill. It has happened at several landfills though. Ironically they think the root cause is pulling too much of a vacuum on the landfill gas collection system, to control odors, which pulled air from the surface down into the trash, creating essentially a huge hot compost pile, which then went anaerobic. It was able to sustain itself due to the excellent heat insulation provided by the earth, allowing the high temperatures to persist. This nightmare is one reason to minimize our use of landfills. Republic has spent over $100M on it over the last 5 years. Not even exaggerating. Speaking of the thread title...dark liquid? About 200,000 gallons per DAY of leachate.