Hello!
Piperazine (the active ingredient in Wazine) is the only de-worming drug approved for use in poultry used for meat or eggs. If you use anything else please be very careful, and don't eat the eggs for a while afterwords!
Ivermectin as a paste for horses is in a much higher concentration than a bird can handle. Since using ivermectin to de-worm birds is an off-label use, it is difficult to find any kind of dosing recommendations. I'll keep looking and see if I can come up with anything.,
Although roundworms are gross, and the fact that they can (very rarely) end up inside an egg completely skeeves me out, they generally aren't a problem in healthy adult birds. Chickens over 3 months of age seem to develop an immune resistance to them. Young, weak, or susceptible birds can develop weight loss, signs of blood loss (pale combs) and potentially get an intestinal blockage with an ascarid (roundworm) infestation.
Pumpkin supplies a huge amount of roughage, and physical "pushes" the worms out of the intestine. How well it, or other pumpkin seed/garlic/hot pepper/papaya seed pastes (I've heard lots of different cures) work hasn't been proven, but if the birds don't seem sick and the treatment doesn't hurt, what does it matter? Use care not to give them too much garlic, however.
Hope this helps!