Just nabbed a poison weapon for the first time. I've been looking at the old school wiki and using my previous limited knowledge to try and understand, but I can't figure out why I'm not getting any poison damage on anything.

As far as I understand it, you simply need to do damage, whether it's 1, 9, or whatever and then it will have poison applied 100% every time, refreshing duration with additional hits. Yet I've tried it on four different enemies already thus far, and no matter what I do I'm not getting any green splats. On Outlaws, Guards, Spiders all clustered around the GE, as well as other Goblins. For the Guards and Outlaws I kept stabbing them until they were at 2-5 health left, waited 45 seconds, and they still were not taking any additional damage. Testing on spiders and goblins, whether I hit 1, 2, 3, or 4 - never got an additional tick of damage. I even waited so long that a spider regenerated 2 health just while I was waiting. I'm using an 'Adamant dagger(p)', what am I doing wrong here? 

Poison is not applied 100% of the time. There is some sort of probability (a rather low one honestly, around 25% I think) that an enemy will get poisoned when you use a poisoned weapon against it. In most cases, you will kill the monster before the poison is applied or its damage activates against the target.

Ahh, that definitely answers some of the confusion then. Is it different for p+ and p++, or do they have that same low application chance? 

the difference for + or ++ is damage