Clean the converter well. A cup of water + 2 drops of dishwashing detergent. Run it through the converter maybe 6 times. Then follow up with clean water another 6 times.
Next clean the pen. Go to a drug store and get a bulb syringe. In the baby supplies area. The bulb syringe forces more water thru the pen, so is good for cleaning cartridge/converter pens. Using the same mix above, fill the bulb and stick it into the back of the section, squeeze and let the water/ink drain into the sink/bucket. Do this a few times, followed up by several times with CLEAN water.
Just holding the section under the tap does not have enough water pressure to clean the ink channel of ink.
All inks are not equal.
Some inks can be too wet for the pen. I don't know about Sailor, but the few Noodlers inks that I tried ranged from wet to VERY wet.
And some inks can be too dry for the pen.
Without adjusting the nib to the ink, you are left with finding the ink that will flow at a desired rate thru the pen.