I don't seem to have the knack.
Shoot ahead of where the survivors are going, don't shoot directly at them unless they are running in a straight line away from you. The vomit has travel time so if you shoot it at them while they are running sideways it will miss.
Dont try to follow , just shoot as if you are watering your plants. Her power is long enough to cover pretty good amount of space next to a survivor thus making it impossible to avoid
Try to spray more. Plague as quit a lot of "ammo" so you can shake your head from left to right quickly to cover more space and get more hits. Especially while you are using her red vomit this can get you more hits. Also sometimes aim higher, her vomit flys in an arc.
Finally: Aim ahead. Sometimes lack and travel time in combination can get you if you aim right at the survivor. Be generous with the stuff...you have a lot to give...
First of all, I see that you aim quite low. When I use Plague I usually aim more upper and spread my mouse during corrupt purge because even the small puke will be counted as a hit during the corrupt purge. Secondly, take your time when you use your vile purge. You need to charge more and be a little bit more patient. If you act so fast and have little charge, most of the survivors will avoid that so take your time.
Hope that the servers let you get a hit.
Lead more, spray more, be patient, all good advice thanks. I'm too used to playing Trickster and Huntress where ammo is a thing.
Also, the hitbox of puke you see, is not the actual hitbox of it. Have fun
Best dbd sentence is be generous you have a lot to give hahahaha