I haven't grown tomato's in the 4 inch pipe, but I have grown some real tall sugar peas in them with no water flow problems, aside from the occasional roots getting into the overflow tube (that was simple and easy to clean out). I just popped it off from the outside, and stuck a knife in and cut them off. Then just stuck a small piece of wood in to push them back. I have learned that general rule of thumb, make the opening for overflow side twice as large as the inlet side. I attached some pictures of the root system in 4 inch tubing from my peas.