When using a syringe I first pull the plunger completely out and then smear a little
juice on the rubber partn(just to lube it), then I simply squirt my
juice into the open end of the syringe (keeping the needle on the other end) then insert the plunger. Insert the needle to the bottom of the carto and squeeze in a little juice, rotate the carto a little and squeeze a little more juice, then only insert the syringe about half way into the carto and inject juice rotating it same as before. When it starts to get full you will see it start to saturate the wicking material. I then top it off by dripping juice directly in the top. If the little tube in the middle of the carto gets juice in it I stick a straight pin into the tube from both ends to unclog it. You can slide the straight pin in and out of the tube and wipe off the excess juice and your carto will stop gurgling. After I fill a carto using a syringe from then on I just drip juice directly from the bottle into the top of the carto to top it off, so I only use the syringe on the very first filling. When filling cartos this way you start
vaping immediately because the carto is saturated throughly from the bottom up. This is a very easy process and the only other thing you have to do is rinse the syringe with hot tap water.