Like for many eels as yours, do become more active when its night for which they feel that using the cover of night along with their sensitive sense of smell as for if you only had this eel in this tank, it would appeared out more often. For ask around people who own a goldentail moray, that if they keep a well stocked aquarium, this eel will mostly only dash out when there is food. For myself, I keep a pair of these eels in a 70 all by their lonesome, and they swim around much into the open.
I called again the animal hospital, and the doctor who is in charge there has not returned my call as yet. For other then tearing the tank apart, might be your only option. But please wait and see if the doctor here can give some thoughts on the situation before doing so.
One other thing which troubles me is that, this eel is quite long and if the doctor here can suggest any sedatives for the eel. The eel might wrap its body around a rock other then being inside of its lair. But still if there is something to give the eel to make this easier and you not have to tear the who tank apart in trying to remove the eel.
So can you wait to see if the doctor can make this a easier job? If he tells me that there be nothing to do here, I will post then that you can pick the time and day to remove the eel from this 125.
Can I ask you in how long you had this snake eel, and at what size it was when you gotten it? Also, what you been feeding it? And can you post a pic?
Just before I was to post the message above, I tried calling again and had a asked the doctor there the question and this is what he said. They need to sedative the whole tank, that he knows of nothing else what you can do and he as well as myself had come up with one other who might know if you can place some sedative in the eels food. But you need right now is patience for the idea we came up with is that you can email Charles Delbeek who is at the Waikiki Aquarium in Hawaii.
Sorry I nothing better to tell you on this and when the time comes to remove this snake eel, wear protective gloves in case of it biting, for a net here aren't strong enough I believe to handle the eels weight, maybe. I handle it as if a snake on land, get it about near the neck and about 12-15" at the other end of its body.
Buddy