I'd recommend using a silicone coupler or radiator hose instead of this flexible rubber one
Built a Boost Leak Tester for around $15.
Boost Leak Tester
The first one I built had a rubber coupler that attached to the turbo, but that blew off at 15psi. This was most likely because of the rubber "spacer" ring that the T25 turbo uses so the intake fits on the turbo. Any other turbo should be able to get a rubber coupler to hold up to at least 16psi.
Should cost around $20 or so if you get a silicone coupler and T-bolt clamps.
If you have an extra boost gauge, hook it up so you can monitor the test pressure in the engine bay. Otherwise, you will need a friend to tell you what pressure it is at and when to stop. Plug the line going to your boost controller and start pressurizing the intake..
Do you have access to an air compressor? A tire pump just didn't have enough flow to test mine. The first leak was too bad. When using an air compressor, be very careful to slowly fill the intake. It is easy to blow the boost leak tester 30+ feet away from the vehicle. Always keep an eye on the test pressure. Start with 15psi and then move up. If you run at 16psi, there isn't much reason to test past 20psi.
Here is the original VFAQ page for building an intercooler pipe tester
You have a couple different options.
This is not the best choice because turbo seals can leak when the car is not running. It can also be difficult to track down large leaks this way. It just tests too much at once. Once you have fixed most of the leaks, then it is not a bad way to quickly test for new leaks. Just keep in mind that a bubbling oil sound in the oil pan is usually just air slipping past the turbo seal. Bypass the turbo and re-test.
This is the best way to test the first half of your intake. You can move the cap further downstream if you want to test your intake in even smaller portions.
Most people will be suprised at the number of leaks this test will find. Have fun. Clamp off the PCV line if you suspect it is leaking and continue testing. Some people find that their boost gauge line and even the gauge itself is leaking. Don't forget to check inside the car during this test.