A good rinsing in clean water is all you need unless this is coming from someone's garage or attic.
If there were questionable contents at one time and it needed to be REALLY cleaned, I'd use bleach water and then rinse very well, then the dechlorinator should take care of risidual bleach...but this would only be in extreme cases. Vinegar is a safer cleaner if you feel you need it, but don't use soap.
Soap and detergent are not good for fish or plants. And, you can get the tank clean very well using plain water, or a little bleach, or even baking soda. If you use bleach, rinse it well and use a dechlorinator like Prime in the rinse water.