Everday after I've used my carpet extractor I quickly wipe down the outside with a damp towel. I use a strong spray of water and I rinse out the reclaim tank to flush out all the dirt that settles on the bottom. There is a wire filter over the air intake in the reclaim tank and I pull that off and clean anything off that's stuck to it. I then will suck all the water out of the reservoir.
Once every few weeks I'll put a couple gallons of water in the reservoir, start the pump, and then fill the whole system full of vinegar including the 25' hose. I will then let it sit a few minutes and then put a rubber band around the handle to have it spray all the vinegar out of the system. I then rinse the reservoir out with water, fill it up a little, and let the system pump that water out. While it is doing this I will spray the reclaim tank down with some soap (I just use my carpet cleaner *shrug*) and wipe the sides and bottom down with a shop towl to scrub it a little and then I rinse the reclaim tank out.
It's a lot of work but next to my truck it's the most expensive piece of equipment I have. Also, if you don't clean that reclaim tank out well, then it'll start to smell like a sewer.