I bought a used Atari 130XE in a bad shape:

After doing my job:

Here you can see some photos about the process:

I used the dishwasher to clean the case. But attention you have to remove it during the cleaning process before the dry process starts. I suggest a time around 10-15 minutes.

After removing I cleaned the case with water. If you want to speedup the process you can use a hair dryer. For strong dirt you can use ethyl-alcohol. A tooth brush does a good job too.

For cleaning the keyboard I used plastic cleaner with a brush and removed the water with a pressure air compressor.

Have fun