It is not recommended to add Dawn dish soap or any other non-Kärcher detergent to the water reservoir of the Kärcher OC 3 Plus. Here are some reasons why:

- Kärcher recommends using their own cleaning detergents for optimal results and to ensure the product functions correctly. Other detergents may not be tested for proper dilution ratios and cleaning results.
- Using non-recommended detergents can lead to issues such as foaming, clogging, or damage to the device's components.
- The manual and product specifications advise against using non-Kärcher detergents to maintain the warranty and ensure safe operation of the device.