The correct answer is that only approved equipment and procedures should be used. In a pressurized aircraft, a leak is rather easy to know you have. If you’re flying above cabin altitude and you have a leak inside the pressure vessel, your altimeter will read roughly cabin altitude and your respective airspeed indicator will read low.
In a smaller aircraft, there really isn’t a good way to know. Tapping into a line with a tee-fitting may prove good, but what about the disconnection of the tee fitting and the subsequent hookup of the aircraft lines? How do you “know” they are ok?
There is one trick that I have used as an A&P for hard to find leaks. The lines in most aircraft are stainless steel. Provided the respective endpoints are removed and capped (instruments, etc), I will hook dry nitrogen up to the static port and run it at 20-30 psi and listen for the hissing noises.
20-30 psi will not damage a stainless steel line or the fittings. The biggest risk is ensuring every instrument is removed as you could damage them.
Using anything other than dry nitrogen would be a mistake, though, as other gas with moisture could induce moisture into the system.