The earliest instance seems to be this post; beyond that your guess is as good as mine.

This image demonstrates at least a cursory concern for composition. The focal point of the image is not the center of the frame. There is a consistence in the angle and space allotted to the outside-edge-of-the-tub/floor and the inside-of-the-tub/tile wall. The model is watching what is happening in the frame not searching for approval from the viewer. She is presented nearly whole in the frame. Lastly, the flash is exposes the white fiberglass perfectly, stopping short of overexposure.

I love that this young woman is still wearing stockings and cute top. Along with the polish on her nails, the image retains color that levels out what would have otherwise been the tub being too white or her skin blanched.

There is clearly an urolagnia element to this scene. Yet it is– for me at least–mediated by the geyser-like appearance which although certainly urine echoes tropes surrounding female ejaculation.

In other words, some forethought and technical skill went into making this image. It’s gritty and transgressive but quality is not sacrificed just because its content features fetishistic elements.