I wouldn't toss an old aquarium out in the trash. Even if the thing isn't of great value or interest, there probably is someone out there who can use it. I have known many animal people who seek out used equipment when possible. It saves money, and it's probably better environmentally to use something that already exists than toss out something and have it made all over again.
Even if an aquarium leaks, it could still be useful as a glass case to hold dry-land animals.
I knew someone who worked for a nearby Goodwill. Stuff like aquariums came through regularly, and was priced at the "who really wants this junk?" level. She knew that it was worth a lot more, and twisted the store manager's arm to allow them to be repriced. The new price was quite a bit higher, although still reasonable. Much of the time, stuff sold quickly--often in hours.