This is tempting, but I'm going to pass on it, and I bet someone else here would be interested...
On my generic steel 4-cup and 9-cup pots, all the tube diameters are small - about 8mm. This includes the water tube feeding the funnel, and the tube going through the upper half.
Occasionally someone will show a photo of the inside of their pot, and the diameter looks quite a bit larger. I wonder if this varies a lot by brand and size of pot. I would expect it to affect the pressure.
I did some searching here, and couldn't find a previous discussion about this.
