Stick the needle in the amp and pull the plunger back. Am i missing something here? Maybe you want to know how to open your amp? If so, score the neck with the edge of a file and snap the top off, might want to protect your hands with a towel or use a bic pen top, or just buy and amp opener.
wipe the amp with a sterile wipe, snap the top off, stick the needle in and withdraw the oil.
i usually wrap the amp in the sterile wipe and push the top with my thumb and it snaps right off. are your amps already scored? do they have a white line round the neck?
if they are they will come off nice and clean and easily.
I've had glass go into my amps numerous times. I still withdraw but leave a little at the bottom. (may not be safe but I never had a problem). The glass will sink, you will see it at the bottom if you hold into the light. Most of the time it will break clean though. Farmak Prop was the only one I had problems opening sometimes.
i have opened about 20 of my amps so far. some have white lines and some dont(different batches). the ones with white lines are scored and snap very easily, the ones without lines arent as easy so you have to push a lot harder but i have never had a problem they usually break clean off too. what brand of test are you using? iranians? icn?