If you have a vet that will do the test for you, then I would do that. Drinking a lot when it's hot can make the droppings runny, but since it's been going on since May that may be a less likely cause. Corid will treat for coccidiosis, but not the other types of worms they can get. You can use Safeguard Liquid goat wormer, Safeguard horse paste, or Valbazen wormer and dose each bird orally. The Safeguard would be .23 ml per pound of bird weight, and since you don't know what worm it might be then it would be done 5 days in a row. The Valbazen would be .2ml per 2.2 lbs of bird weight (weight in lbs/2.2 X 20mg / 113.6 = dose). Many round to .5 ml for a standard sized bird, you would dose the Valbazen once, and then repeat in 10 days. Safeguard is usually available at Tractor Supplies and feed stores, the Valbazen often needs to be ordered on line, but with Covid many places are out of stock. I had to order my last bottle of Safeguard. Most of the time you will not see worms in the droppings, the test looks for the eggs which are microscopic. Occasionally you might see a roundworm expelled, or tapeworm segments, but not always, and most you will never see at all. Safeguard and Valbazen will take care of most common worms they can get. If you knew it was tapeworm, then a product with praziquantel is most effective for those. If it is worms, then you may or may not see dead or dieing worms in droppings after treatment. Sometimes they are expelled, but sometimes they are just digested. If they don't improve with worming, then other causes will need to be considered. Hens over the age of two are prone to reproductive problems also, and a symptom of that can be droppings built up around the vent feathers.