Any time you change water velocity you will have a loss of pressure. Upon entering the reservoir, the water will "disperse", losing its concentrated velocity profile that existed in the tube. It must re-establish this when leaving the reservoir. As a conservative estimate, take the water velocity, square it, and divide by 2 * gravitational constant. With the right units, this will yield the head loss for the combined entrance and exit loss measured in height of a water column (feet of water, meters of water, etc.).
It will be a fairly low number, but real.
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