First, I've read though questions Soldering Iron Maintenance and Going through Soldering tips quickly and was unable to solve my problem. I have recently (as in less then a month ago) obtained Multitip 25 ERSA Microsoldering iron with 0172BD/10 tip.
From the start I had problems wetting the tip. I tried everything but solder just wouldn't flow over the whole tip. I later found information in one of manufacturer's catalogs that I should wrap solder with flux around the tip and then turn on the iron. After few tries, I managed to get a big part of the tip wet (and it was working great), but one small part wouldn't wet.
After some soldering I decided to try to get whole tip wet and obtained 0TR01/SB tip refresher. After using it according to the manual, the whole tip was covered in black substance which should be easily removable, but it isn't.
Now about half of the tip is contaminated and about half seems to be working (I managed to clean the working part).
My question is: Is there any other way to clean the tip? Two things from questions I linked I didn't use were dedicated tip cleaning mesh (couldn't find a source of them in my country) and flux outside the wire (because I don't have any at the moment) and how to decide when a tip is dead and needs replacing?
Also, how do the tip refreshers feel (I'm assuming that they are more or less all alike)? I often find them described as paste, while the one I got is solid (but melts when in contact with hot tip).