[Skulemate]

You are correct Ewan, using equivalent lengths typically yields a rough solution, though for what I was taught to do it is typically good enough. Keep in mind that I am not an expert on fluids by any means (I am a student civil engineer specializing in concrete materials) though I have had some formal training in the subject. In any case, there are more exact methods than using equivalent lengths, but for what we are doing I would question whether or not the more complex solutions are warranted.