I made some air hoses.  This was fun!  I started with the 4 mm hose barb on the sensor, so found some 4 mm ID, 6 mm OD air hose on amazon.

Uxcell a13080200ux0301 Blue 9M 29.5Ft 6mm OD 4mm ID Polyurethane PU Air Hose Pipe Tube

The HRV has little ports in it, so picked up some air needles...

Golvery Ball Pump Needle Pack of 20 for Sports Balls, Stainless Steel Inflator Needle Set Adapter, Dual-Port Design, Perfect for Any Football, Basketball, Soccer Ball, Volleyball or Rugby Balls

To keep the hose rigid at the interface to the needle, I got some 4 mm OD steel tube...

uxcell 304 Stainless Steel Round Tubing 4mm OD 0.4mm Wall Thickness 250mm Length Seamless Straight Pipe Tube 4 Pcs

Here, I placed the tube in a vice, and cut it using a pipe cutter.

Then, I wrapped a small amount of tuck tape around the metal tube to raise the diameter so that it just fits in the air needle.

Then, slid the metal tube into the air hose, and the air needle over the metal tube.  Next, I placed shrink wrap over the whole thing with a bit hanging over the air needle so that it holds the whole assembly together.

Here is the code for the raspberry pi pico on GITHUB that I wrote:

GITHUB

Here are the air needles/hoses pressed into the measurement ports of the HRV, and the PICO board dangling off of the sensor (maybe I need a 3D printed case...).

So - the pressure drop across the HRV core (stale air side), is sitting at about 17.5 Pa.  Joy!  It is great to be able to measure small pressure drops like this with a barebones setup.