Depends on the actual geometry of your setup.
You can imagine it as a smooth metal bottle with approximately 10cm diameter and 30 cm height, with the sensor on top.
Yes. Easy to test.
Of course, but I do not have the components, yet. And I wanted to get some advise, before ordering them.
The ultrasonic is going to “hear” the first reflection back to it.
A ribbed culvert will bounce the signal right back, while a smooth wall tube will might carry the sound far, far away.
I am not so familiar with inner working of these modules. So maybe the better question is, if the bounce of waves will be strong enough to trigger the sensor.