Stand a pen in a glass of regular water. The ink, being heavier than water, will start to drain out of the nib section. This is the best way to clean your pen.
A fountain pens is an amazing creation, look after your pen
Your pen, whether a ball point, mechanical pencil, roller boll or fountain pen should receive good and proper care.
The finish of the the pen is specific to the type of material. As a general rule use a soft cloth and water clean. Avoid cleaning fluid as it could damage the finish of the pen.
For sterling silver trim, clean the silver with a silver polishing cloth. If you have to use silver cleaner, put some on the cloth and then rub the cloth on the pen. Don't put silver cleaner on the pen itself. It can get into small places and be difficult to get off.
Lacquers are often though as being delicate surfaces, but they are quite durable. Use a moist soft cloth to clean the pen and avoid abrasive cleaners or chemicals.
If you are not going to use your for for a long time, it is best to not leave the pen filled with ink. That means if you have a number of pens, you will need a little disciplined in terms of rotating the use of your pens. If you are not going to use the pen for an extended period of time, empty out the ink. Give the pen a flush with water.
If you are going to store a fountain pen for a period of time, then flush the ink out of the pen. But if you don't then have the pen stand vertically. This means the nib is pointing up in the cap of the pen. Any ink will flow down the tiny channels back into the pen rather than into the cap of the pen.
It is a good idea to give a fountain pen a good flush every month or so. This means, pushing in and out the converter or piston while hold the nib of the pen under a stream of water. Then dry out the nib and ink mechanism with a towel in a glass, standing the pen, nib down. The paper tower will help to pull out the water from the nib and feed chambers.
When cleaning a pen, use lukewarm water, never hot. Hot water could impact seals in the pen.
If the pen is clogged, and after a flush of water there is still an ink flow problem, then I let the nib section stand in a glass of water for a couple of hours. This is okay for most modern pens. Some older vintage pens may have materials that can be impacted with standing in water for an extended period of time. This is the case with But do not do with pens made from rubber or casein pens (it looks like plastic but made from protein). Prolonged period of time in water could damage the pen.
I am always amazed at the trail of ink that flows from the nib as the pen sits in water.
If you have not used the pen for a while, and you go to write with it and no ink flows, don't just press harder and harder on nib to get the flow going. You may damage the nib. Make short strokes diagonally across the paper. Use the same pressure as your write. The strokes will activate the flow. If nothing happens, then dip the nib in some water.