Hose extenders come in two basic types.
Pressurized and Non-Pressurized.
The non-pressurized ones have pin and long rod that runs from the outer end with what looks like the normal valve core. Pushing on the outer valve core stem pushed the rod that is supposed to then push the valve core on the valve stem on the wheel. Sometimes it is difficult to push on the outer end enough to actually open the real valve core on the stem on the wheel. If you are having problems adding air or getting a good pressure reading that is probably your problem.
Pressurized hose extenders press on the tire valve stem and open the primary valve core in the stem on the wheel. You can hear a little air leak as you attach these hoses but the leak should stop once the hose is properly tightened.
Proper tightening of the hose extender would normally be 1/2 to 1-1/2 revolutions after air leak has stopped. You should not need tools or pliers to tighten the hose sufficiently. Over-tightening can damage the very small O-rings in the valve system.
Outer ends of extenders need to be solidely
attached. Especially longer (4" +) extensions.
Here is my current setup.
This shows the angle bracket that is riveted to the metal wheel cover and my TPM Sensors on the outer end. This took some figuring as you do not want the hose to touch the wheel or hub cap. In my case I needed a secondary 120° angle metal extender to get the hose properly oriented.
Here is my previous set-up.
NOTE the picture was taken without my TPM sensors installed.
I had 28,500 miles on this prior system with no problems or leaks. Since I have TPMS, if there are any leaks I would get a warning as soon as I lost 3 psi so am not worried about low pressure tires.