yes you should use a tube,not a straw, for the throttle pushrod.
like Mr67Stang put quite clearly, the tube prevents any flex or binding in the wire or rod.
example: the fuel tank moves in the tank compartment and rubs up against the pushrod causing servo to strain, and drain battery quicker than what you would normally expect,it's surprising how fast a typical battery drains down to nothing.
is it worth the risk, not on my planes
better be safe than sorry whats a little bit of pushrod tube ?