Cartomizers have become quite a viable alternative to the standard atomizer and cartridge for a lot of people. While they were originally designed to be disposable when empty, most users refill them multiple times. In most cases, the cartomizer flavor becomes unacceptable long before the carto fails completely. Switching juices can also be a problem, as the filler will always have a little residual juice. Cleaning cartomizers is not as simple as cleaning an atomizer or cartridge because the filler cannot be removed for either rinsing or drying. Running water through them works to a certain point, but drying them can take a lot of time.
So what to do with all of those used cartomizers? Fortunately, a vaper who goes by 0smitty has posted a great video on YouTube showing a novel way of cleaning and drying cartos using an oral syringe. The syringe is readily available at Walmart or the drugstore. I found this one at Walgreen's. They come with a bottle adapter that has an indentation on the small end that fits securely onto 510 and KR808 cartomizers. It's like they were made for this purpose.
The process that 0smitty illustrates in video consists of pushing the mouthpiece end of the cartomizer into the bottle adapter with the syringe on the other end, then dipping the battery end into hot water. Pulling on the plunger draws water through the carto into the syringe, pushing it squirts the water through the carto and back into the bowl or pan. Repeat this process five or six times to get the filling clean. Then pull the carto out of the water and vigorously pump the plunger 40 times or so. This forces the water out of the carto and actually does a pretty good job of it. Putting them in the oven at 200 degrees for a half hour or so will further dry them. You end up with a nice clean carto, ready to fill with your favorite juice.
Edit: After this article was written, Smoktek introduced a Cartomizer/Atomizer Cleaning Kit that accomplishes the procedure described above, but with some adaptations that make it easier. The syringe in this kit is equipped with rings for the thumb and fingers that make it easy to grip. The kit also includes small sections of tubing that make fit snugly onto both regular and mega cartos. It works great and makes the process even easier.