How to get yellow out of plastic bathtub?

https://www.hunker.com/12002247/how-to-clean-a-yellowing-fiberglass-tub

Hi there, here's another idea. Hope it helps. https://homeguides.sfgate.com/whiten-yellowed-plastic-tub-surround-34638.html

I love Wet and Forget Shower Cleaner sold at Lowe’s or Amazon for about $12 with many uses., not just a one time cleaner. We have a fiberglass shower and it works miracles. You may have to scrub a little in the beginning depending on how bad it is....but on ours it looked brand new again after seven years of never good results with other products.

Unfortunately older plastic tubs and surrounds turn yellow with age. Some client's tubs I've been able to lighten using either a 10% bleach water solution in a spray bottle. I've also seen folks use the the Oxiclean mixed into a paste.

Try Zud cleanser. I use it for my hard water with iron. Make sure you get the creamy cleanser.

Bar Keepers Friend spray worked better than anything for my tub with hard water and rust stains. Spray, let it sit for a minute, then scrub.

Use toilet bowl cleaner. It will clean it.