This is the 100ml Rotring Cleaning Fluid for Technical Pens. Product images shows that the cap can come in different colours. Mine's the white cap.
I think technical pen cleaning fluid is really useful for anyone who uses fountain pens, more so for those who use a lot of them. It's great for cleaning the pen and clearing ink clogs when water just won't do.
This is my Hero fountain pen which I had not used for a while and now the ink's not flowing well because of the clogging. It's still easy to clean off surface stains like this. However for clogging, more drastic solutions are required.
I found a small tray and soaked the pen nib in the cleaning fluid overnight.
You can find a smaller tray to save the fluid. I think I used too much here.
The is how the nib looks after I took it out the next day. All the ink has dissolved. The nib and pen now looks and functions as good as new.
For seriously clogging, I would suggest first using water in a convertor to push through the filter system. Then use the cleaning fluid to push it through several times. I reused the flushing fluid several times. After that, I left the nib in the cleaning fluid overnight. For a brush pen that had serious clogging, I did this procedure two times.
It works and it's great.
Here's a video of the process.