Here's a thought. Try putting the Horse manure in a feed sack, then place it in the water and let it soak. Sorta like a tea bag effect. I do something similar with compost, and make a compost tea. Then drench the plants with the nutrient laden water. Its best to lift the bag out from time to time to extract more nutrients. A burlap feed sack works best, but a plastic woven type will work. That will help eliminate strainer process.