i am not supportin you keeping an eel in a nano tank, but to help it stay alive i offer my answer:
o to your LFS and find some filter sponge. Its about 3x3x12. then cut the sponge so it is 1-2 inches tall and covers the filter system. basically, a sponge lid over the filter. when you close it, the plastic splash cover on the lihts will push down on the sponger, sealing off the filter system. i had to do this because my goby kept jumping.