By chance I found a Pitot Tube simulator on the internet. Using this you can block the drain port, etc, and study the effect. I don't know how accurate the simulation is, but the pitot tube is rather well described by bernoulli's eqn.
Try it. Here is a link:
luizmonteiro - Online Simulators - Pitot Static System Simulator
Perhaps it will make all agree to on what can happen.