There is a line of products specifically to identify and remove stains. Jack's Magic.

Whether it's the steps, the liner, etc., whether the stains are yellow, brown, rust, etc.

The Step Stuff will take care of the steps.

For the liner, white accessories, first, we identify the stain, using the Stain ID Kit's 3 bags, then according to which bag removed the stain, the product required is mentioned on the bag.

The Eliminator.  It removes metals in the water (before they stain), but it's a very different product, nothing like it on the market.