My experience is limited to the DSE 901's ,
and with these carts (not sure about other models)
The small space that holds the filler material is sealed and the only way that the juice can travel is by being "wicked" into the attomizer mesh.
I've used the old style and new style 901 carts...The old style 901 carts had one large "air passage" the newer style has a smaller passage on both sides of the cartridge.
The way that juice can get to your mouth is by way of these "air passages".
It first goes into the atty , and then (any unvaporized liquid)by way of suction turns around and makes its way back towards the mouth through these passages.
Because of this I find it necessary to periodicly blow through the mouthpiece (rather than suck)
as you do when vaping in order to clean out any excess
juice in them.
I also take all my carts apart once a week and put them in a 50/50 solution of water and isopropol alchahol and swirl them around a bit , then let them sit for 1/2 an hour (in the solution) to disolve any juice that may have thickened in
the passages.
I Swirl around once more,then dump the "cleaner" then
fill the container back up with some very warm water and swirl again to rinse ,I then towel them dry,
then allow them to finish drying by air.
It's a bit of work but it keeps the air passages clear and free making for a pretty easy draw.