If you dont want to have to pay for shipping for that carto cleaner syringe thing you can pretty much just make your own for only a few bucks. Go to a pharmacy and buy an baby's oral syringe. It wont have a needle, just a dull plastic point. It comes with a rubber top that you put onto the end of the syringe. The rubber part is really made do be used as like a small funnel that you put into a babys mouth and then administer the medicine, but it actually works really well to clean a carto. The top of the rubber part where the liquid would come out has a pretty big hole. It happens to fit a 510 carto perfectly. It will be alittle tight putting one on the first time, but once you get a carto on it will stretch a tiny bit and they will go on easier. You stick it on the mouthpiece side. (make sure the rubber or plastic white cap is removed). Once a carto is on there you can hold the rubber part on the syringe and get some really hot water is a cup or bowl. Then carefully suck some hot water up thru the battery end with the syringe and push it out into the sink or another cup. The rubber part will stay on the tip of the syringe without holding it but I find if you are pushing the water out of the carto quickly the rubber part can fly off so I just hold it with one hand and push and pull the syringe plunger with the other. You can do this a bunch and bits of juice gunk will come out and open up the airhole. You can also use some PGA or vodka as well to help clean it. Then take them out and give um plenty of time to dry. If your impatient and want them to dry faster, with the carto still on the syringe, push and pull the plunger in and out very quicky into a sink. This will force air in and out and will get a lot of the water out. If you really do it well I have actully filled a carto right after doing that and vaped it and it worked absouletly fine, but I would recommend you still let it dry for a few hours at least. If you do that make sure you def hold the rubber part thats holding the carto onto the syringe bc when you force air in and out quickly it will prob shoot off. I only recommend doing the quick dry part if your REALLY deperate or something. Doing that can potentially break a coil or something and ruin the carto. Ive done it with a few just to try it and they were fine but my buddy has broken a coil doing it, so be careful. It safer just to let them sit and let them dry normally.
Its a cheap way to clean them and it works pretty well, and you can get those little kid oral medicine syringes many places. Its basically the exact same thing as that carto cleaner from Smoktek, but the cleaner comes with 2 different size tube parts that come with it that can hold a few different size cartos. If you use 510 cartos though the oral syringe holds them perfectly so this work just as well, and its cheaper and you wont have to pay for shipping.
If you go onto SmokTek's website, and look up that cleaning syringe, they give you instructions on what to do. Its basically what I just said above but its alittle more detailed so you can follow those instructions exactly and achieve the same results.
Hope this helps!
Goodluck!