Welcome to the sight, keeping eels is not difficult,if you have dockspace they can be kept in a 5 gallon bucket under the dock,drill a series of 1/4" holes in the bucket to alow the flow of water,weight the bucket witha brick,the type of bucket with a screw on cover ,like the ones used for pool chemicals is best,but a standard snap lid will work.
if you must keep them at home,the more surface space the better, a plastic 55 gallon drum laid on it's side on a stand works well,remove a "door" from the top(the old side of the drum) a section of fireplace screen or 1/4" mesh wire makes a good cover.
A large capacity air pump and a pair of air stones will keep them happy.
Change 1/3 of the water every two or three days,when adding new eels watch the water quality closely,sometime new eels purge themselvs when added to the tank and can foul the water,I purge all new eels in a seperate tank for this reason.
To aid in the water quality I recomend cleaning the airstones every time you do you partial water change as the eels will tend to ball on the stones and slime them up,simply scrub the stones with a little scotchbright under running water.
One last thing,I have a screened overflow on my tank,so all I do is turn on the hose and let the water run a few minutes every few days.
Keep them in a cool place and they will be happy,if the weather gets too warm a large block of ice can be put in the tanl to control the temp.