since I have not found anything similar than this, I have made a design.
I have used this for a test cycle at my laundry. Now I have found out, half amount of washing powder will give the same result. This helps saving money. Also, I can insert one spoon in every box of washing powder, so I don't need to read the small text at the box daily.
easy print, no support. Parametrizable in openscad.