I recommend pulling both ends off every 3 years or more. Some things will end up in the entering side of the barrel but will not make it through the tubes like tower fill, birds, squirrel bones, etc. Yes, these are all things I have found before and more. These items will not plug up a tube from the inside...they will plug up the entire tube itself preventing water flow and tube brushing from the return head won't get rid of them.
[QUOTE=jayguy;16530631] Some things will end up in the entering side of the barrel but will not make it through the tubes like tower fill, birds, squirrel bones, etc. [QUOTE]
Also, the screwdriver that found its way there and ended up, blade first, in one of the tubes. Where it rattled around until it wore a hole in the tube, resulting in a chiller full of water and with a grounded motor (semi-hermetic, direct drive). A co-worker found this exact scenario once. Just to give the OP an idea of how important this is.
OP asks a loaded question-the process of pulling both heads requires a working knowledge of that job-such as water quality, tower quality,and biological debris. (i used to pull both heads on some 2500 TR OM's because of the oak trees by the towers)