Here is another fountain pen cleaning video. It is long. If you can listen to the video and look at the screen when you hear the buzzing sound of the ultrasonic cleaner, you will be able to understand what I am talking about.
I said in the video that it costs less than 3,000 yen, but the model I bought cost 3,755 yen.
I think it is safer to buy one from a well-known manufacturer.