Question: If "reek" is used as a term to describe something that smells bad, what word of equivalent meaning would describe something that tastes bad?

Answer: 
Perhaps "**smack**" would serve. This meaning of the word is defined by [oxforddictionaries.com](https://en.oxforddictionaries.com/definition/smack) as

> 
> Have a flavour of; taste of
> 
> 
> 

and 

> 
> Suggest the presence or effects of (something wrong or unpleasant)
> 
> 
>
Not sure that there is a comparable word as 'taste' by itself (even in context) does not have an alternate meaning that implies unpleasantness. 'Smell' can imply unpleasantness.

Example:

"Something smells."
"Somethings tastes."

..and as an adjective can in fact imply pleasantness...

"That is smelly."
"That is tasty."