failed smog because of fuel evap leak

[fixkick]

Hello Vidas, and all I am not an expert, but I understand you failed emissions test. I am guessing its California.
1995 and older vehicles require an Low Pressure Fuel EVAP Test. They do use Nitrogen gas because it is an inert gas.
They test the the EVAP system by pressurizing the system at the filler neck with a hose the goes through adapter that wil be similar to the gas cap that is tested separately.  They pinch the hose at the EVAP canister to seal the system.  For diagnosing  EVAP leaks I have seen licensed Smog Repair Stations use a Smoke Machine that puts visible smoke in to the system that will come out of the area or areas that are leaking. It cant be that expensive to use the smoke machine and then you could fix yourself. 

Hope this helps

Regards

this post is old. 2016  (1995 car)
yes,  all that is correct.
leak down tests, are many , even soap bubble tests,  and smoke machine.
the 95 is way more simple than the 96 with , 3 solenoid valves to fail.  
finding leaks here can be daunting..

see list below, of causes..   and more top of tank rust, and vent boxes on top of tank made of plastic that crack.  nothing here is easy to find, long hard work.
there are 2 DTC errors in 96+ below and 443,  there ar 2 tests done, but not on yours.