After the device withdrawal, the common sense would recommend to wipe the skin and the suction cap before reapplying. Not throughly, just really quick. I doubt any venom will be in the syringe, just air. If no Sawyer Extractor is available, the mouth sucking technique, I believe, is still more than nothing. At least much better than those rubber cap based kits available on the market (though, one may need some practice sucking hard).

NightHiker: The venom in the mouth is nothing compared to venom in the tissue. Just spit once in a while if you wish so. But if nothing else is available, it's a chance. Whatever doctor said (Ok, - IMHO).