TSC usually carries Wazine 17. Following are the dosing instructions from TSC website:
Directions for use:
Begin worming at 4-6 weeks of age and repeat every 30 days to break the large roundworm lifecycle. One pint will treat 800 turkeys under 12 weeks of age or 400 turkeys over 12 weeks of age, or 1600 chickens 4-6 weeks of age, or 800 chickens over 6 weeks of age. Do not use in chickens producing eggs for human consumption.
Chickens: 4 to 6 weeks of age: for each 100 birds, use 1 fluid ounce (30 ml) of Wazine-17 in 1 U.S. gallon (3.8 liters) of drinking water. Over 6 weeks of age: for each 100 birds, use 2 fluid ounces (60 ml) of Wazine-17 in 2 U.S. gallons (7.6 liters) of drinking water.
Note the egg withdrawal statement. You should toss any eggs laid for 2 weeks after each dosing.
Wazine is added to the water, the instructions will be on the bottle (1 oz. to gallon of water). Here is more info on Wazine: https://www.drugs.com/vet/wazine-17.html
Pick up your water when they go to roost the night before, first thing in the morning put out the medicated water, so they are thirsty and hungry and take it in. When they go back to roost that night after treatment dump the medicated water.
Wazine only kills large roundworms. If you want a more broad spectrum wormer then Safeguard Equine paste or liquid goat wormer, or Valbazen can be used, but you would need to direct dose each bird. Those two will take care of most common worms, including roundworm. Roundworm is easily picked up in the environment, so you may have to worm regularly to keep them controlled, every flock is different. If you have a vet that will do a fecal test for you (some will, some will not) then I would get them tested a few months after treatment to see if you have any reinfection (worms will not always show up visible in the droppings), and that will help you to determine how often you may need to worm.