Reddit mentions of Koh-I-Noor Rapido-Eze Cleaning Solution, 8 oz. Bottle, 1 Each

https://www.amazon.com/Koh-I-Noor-Rapido-Eze-Cleaning-Solution-30684/dp/B000KNNI24/ref=sr_1_1?keywords=koh+i+noor+pen+cleaner&qid=1571176467&sr=8-1

and an ultrasonic cleaner will do it

I'd say get yourself some Koh-I-Noor Rapido-Eze Pen Cleaner and soak the pen in it overnight, the stuff is designed to dissolve india ink and will come in handy for giving other pens a through cleaning.

http://www.amazon.com/Koh-I-Noor-Rapido-Eze-Pen-Cleaner-bottle/dp/B000KNNI24

OK. First, air might do the trick. most people have something like this:

https://www.amazon.com/Koh-I-Noor-Pressure-including-Rapido-EzeCleaning-3068SYKT/dp/B004BNNKOU/ref=sr_1_3?keywords=koh-i-noor+ultrasonic+cleaner&qid=1559156384&s=gateway&sr=8-3

It's just a small air bladder that pushes air through a syringe end. This should clear most of the ink from your nib while it's still wet. The kit I linked has a small amount of nib cleaner.

If the ink dries, you want to use water first. If that doesn't work, there is Rapido-eze. You want to follow the dilution directions and use small syringes designed to clean these pens.

https://www.amazon.com/Koh-I-Noor-Rapido-Eze-Cleaning-Solution-30684-x/dp/B000KNNI24

Second, you can put the solution in an ultrasonic cleaner and do that. i don't do this every day with mine if I'm doing something over a weekend or something. Only if the nib refuses to cooperate, or i've been going at it for over 10 hours with a particular nib. Any ultrasonic cleaner for jewelry will work. You can get them cheap off amazon or ebay.

Some people just use a hint of dish soap instead of the cleaning solution. YMMV.

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Also, I saw somewhere else you just incorporate a mistake. You don't need to with this stuff. Just put some on a q-tip and lightly blot the ink and it should come off the mylar.

https://www.amazon.com/KOH-I-NOOR-Liquid-Eraser-Bottle-Koh-I-Noor/dp/B01AVOC6HY/ref=sr_1_54?keywords=koh-i-noor+eraser&qid=1559156230&s=gateway&sr=8-54

>bleach, vinegar and other household cleaning solutions,

Those are not good things to put into pens.

A 10% ammonia solution is what you need. Otherwise, Koh-i-Noor Rapidoeze is excellent and will do the trick.

I'm guessing that there is still residue in the feed that is preventing ink flow. I've seen this before with a used VP I bought. I tried everything and only Rapido-Eze did the trick. I soaked the entire nib unit in it for a day, flushed it with water, then let it soak a little longer in the Rapido-Eze. It worked like a charm.

https://www.amazon.com/Koh-I-Noor-Rapido-Eze-Cleaning-Solution-30684/dp/B000KNNI24/ref=mp_s_a_1_3?keywords=koh-i-noor+fountain+pen+cleaner&qid=1566520461&s=gateway&sr=8-3

This stuff works wonders. I had an orange stain on a white shirt and it took it right out. It is also a good investment to change out your pens.

India ink clogs the feeds of fountain pens. It is probably just simpler to buy a new metro than attempt to revive the one you have just destroyed.

EDIT: But if you want to try and fix it, soak the feed in this, scrub it, and you might get it working again.

I just got a bottle of this today after reading and reading on FPN. A 1:4 dilution should do the trick. If it works on India ink, it should be able to conquer just about anything.
Koh-I-Noor Rapido-Eze Pen Cleaner 8 oz. bottle https://www.amazon.com/dp/B000KNNI24/ref=cm_sw_r_cp_awd_EtzQwbSQJ3D0P