Is he pus coming from the nasolacrimal duct ?
If so then it is likely the abscess is in the duct itself, not behind the eye. Until you can speak with the Vet I would continue to bathe the eye with cooled boiled water and try to encourage the pus to keep draining. Gentle pressure around the duct with a warm compress should do this. You don’t want the drainage route to clog up as that will just allow the abscess to fill up again.
I'm not entirely sure where it is coming from, last night there was too much to tell, but it was coming up from his bottom eyelid I think. Today there is not a lot there so still not easy to tell where it is coming from!! Keeping it as clean as we can, I think it sticks his eyelids together a bit and then dries up so we'll keep an eye on that.