Agree with hotrocks. . . . . . . . .
Obtain a bin. Stick your heater in it and using the tank water and transfer everything to the bin. Have an air stone or small power head for water movement.
Flush tank out with freshwater. Fill with freshwater and see if you can find area where it is leaking from. ( you can do two inches at a time also and once leak begins, you know where on tank or area it is leaking from). Use a razor blade and scrape away silicone from that area and clean with rubbing alcohol. Then apply aquarium SEALANT such as all glass, aqueon or marineland silicone)
Allow to dry at least 12 hrs- better yet 24 hrs and water test with tank full. if properly sealed, no leak should be the result and you can then repack your tank. ( now will be the time to re-scape, add rock and enjoy the tank once again).
If you are not comfortable with resealing, you can empty and buy a new tank, this way you are repacking in a couple of hours. Tub and sealant may cost about $29 whereas you can apply that $20 to a new tank