Cartomizerfillinator ....This is by far the best way to clean cartos. I began cleaning cartos this way about 6 months ago.
Then I had seen Vapians vid on filling cartos and thought dahhhh

,...I can fill them up with that method too

When I get about 20 cartos ready for cleaning, I grab 2 16oz glasses and fill them up with distilled water and put them in the microwave for 3.5 minutes....nice and hot but not hot enough to burn your hands. I pop the carto on my 10mil syringe with the battery connection facing out and pull in the hot distilled water and squirt the nastyness into the sink. "I do this
three times per carto". Now I have clean cartos that need to be dried.. You can use the syringe for this as well. with the carto still attached to the syringe, pull and push on the plunger about 10 times to get out all the water you can.
I only do this a couple of times and then I blow out the water with my mouth from the side of the carto you
vape on.....not the threaded end.....blow that out a couple of times and set them on a paper towell with the battery connection down for 24 hours.. WALA! clean cartos

.
I have tried other methods like......putting them in a pot and boil for ten minutes or so...
jewelry cleaners you name it.
If you have not tried the Fillonater / Cleanonater method out...Please do for the sake of the cartomizer