When I first started lashing, there wasn't much information on how to increase the longevity of your adhesive when in the bottle and how to clean the nozzle. Now we know better. As you may know, adhesive cures when exposed to moisture in the air and when expelling adhesive, the best way to ensure that there is not adhesive clogged within the nozzle is to burp the bottle until any air bubbles pop at the end of the nozzle.
Within lash training, it's super important for educators to not only teach application, but to include how to care for lash products, including adhesive. This will save money and increase the bottle life without getting any build up of adhesive around the nozzle leaving you to have to cut the nozzle off to access the rest of the adhesive within the bottle.
Some other ways to ensure that adhesive doesn't build up within the nozzle is to shake the bottle from side to side not up and down.
It's also important for lash retention that when expelling adhesive, dispose of the first dot expelled as this is not fresh adhesive.
If your nozzle is clogged and you have not cleaned the nozzle properly befoe trying to expel more, you are pushing through old adhesive caught within the nozzle with new adhesive from the bottle which means it will be stringy or not expel at all. You may squeeze as hard as possible and this is also not great because the harder you squeeze the lash adhesive, the more air that gets into the bottle which si why its super important to burp your bottle.
In addition, the use of adhesive nozzle wipes after every use and DO NOT COTTON. This is super important because cotton becomes flammable with the adhesive and you may see some fumes like smoke rise when the two come to touch. It's extremely dangerous.
It is also my recommendation to invest in nozzle piercers or spare nozzles so that you do not end up wasting adhesive due to needing a new bottle.