Depending upon what you're feeding, I personally would go with at least 1" regular bulkhead fittings from a farm supply (easy to install, less chance of an initial leak on a rounded surface than the "DIY" fitting) and tie them together with sch 40 PVC. The 1" + allows the water to level in the 3 drums faster. Cut the bulkhead fittings in around 3" above the bottom of the drums. Job done, less than $50 for all.