Heh, I ran out of detergent not that long ago and had to improvise some with an Internet Recipe of baking soda and a few drops of dish soap. Some of plastics came out with a bit of chalky water marks, but the dishwasher itself was completely odorless for the first time. Filed it away in my memory to run some baking soda every now and then.

Oh, if you're in a hard water area (like many parts of the UK), it really helps to use salt! Where I grew up we never used salt because the water wasn't hard, but in London (for example) it makes a massive difference.

All dishwashers seem to have a reservoir for salt but of course people only tend to use it in regions where it's needed.