Pipe Flow Q: Frictional Head Loss in Tank?

[theBEAST]

Homework Statement

This is in the pipe flow section and the solution treats this question like a pipe. Here is the solution:

As you can see I circled the pipe flow equations in red. If this is the case shouldn't there be frictional head loss, h_f, caused by the walls of the tank? I don't understand there solution.

 

[SteamKing]

The velocity of the fluid caused by the decrease in depth as the reservoir empties is so small that any frictional head loss can be neglected.

 

[theBEAST]

The velocity of the fluid caused by the decrease in depth as the reservoir empties is so small that any frictional head loss can be neglected.

How is the question even a pipe though :O