Good news - if it's growing with use it's gooey leftover burnt juice. That seems like quite a bit so possibly it's pretty thick. If you search for carto cleaning there are a lot of good tips. My way is to soak in vodka for 15 min with a condom on the battery end, then blow it out through the battery end, repeat until vodka comes out clean, then repeat with hot water. Search on ECF for Taryn spin - it's a great way to let centrifugal force get the moisture out. I then set it battery end down on top of a light bulb to dry it in about 15 minutes; others bake them etc. It's important to make sure it's fully dry before refilling.
Whenever my draw gets tight I overfill a little and then blow the excess out. What comes out of the battery end is the dark partially burnt stuff. Thinner juices cause less of a problem, I guess because they vaporize more thoroughly.