I like to use 2 parts 91% alcohol, to 1 part windex when I swab between shots leaving the vent open (no pick). Just a drop or two to dampen the patch. This way it dries pretty quick and stops the patch/rod from sticking and blows the vent clear. When extracting the rod pull it rather quickly to suck the vent clean.
I'm lucky with my smoothie, without the rifling in the barrel, and patches well lubed with borebutter I never need to swab between shots (knock on wood). But I always "pick" my vent when loading.
If you're dry patching between shot I'd suspect you're packing the fouling down into the breach and clogging the vent (went through that myself years ago).
Anouther thing I found, if I get a lot of fouling in the barrel after a shot or two I'm doing something wrong. Sometimes changing the granulation of the powder makes a really big difference (I've even had instances where 2F burnt significantly cleaner than 3F--- and vise versa). And of course using way too much powder leaves lots of crud in the bore.
I use ONLY true blackpowder, synthetics may be different? I don't know. :m2c: