Bathtub Gins (also known as compound gins) are not actually made in bathtubs. Whereas most gins add juniper and other botanicals through distillation, these gins add the botanicals by simply macerating them in a neutral spirit and then filtering them out. Because of that, bathtub gin tends to have a golden hue to it.
The bathtub style refers to a gin where all of the botanicals are added via maceration without distillation. There are many gins which add signature botanicals or aromatics after distillation. These would not be described as bathtub gin.