Yellow stains on toilet seat (sorry)

[sergeantmajor]

Our last toilet seat developed horrible yellow stains under the seat. Impossible to shift. Just had a lovely new bathroom put in and the brand new toilet seat is getting the same thing. Yes, I have boys who wee everywhere.
(Some one in a bathroom showroom once told me it was due to not leaving the seat up when using Harpic, but that doesn't add up as it is more yellow in some places than others).
How do I get rid of these disgusting yellow stains? Steam cleaning, cream cleaners and magic wedge of foam from Lakeland have all failed. I've never noticed this at anyone else's house, so where am I going wrong?

Magic Sponge!

Toilet seat going yellow also depends on the seat material used. For example, seats made of polypropylene (basic plastic) has a tendency to yellow over time.
https://www.manomano.co.uk/advice/toilet-seat-buying-guide-6164

Hi,
I've tried the magic sponge, oven cleaner, cif and none work.
If there is anyone out there with a solution I would love to know.
Very embarrassing when we have guests.
Plus these are Villeroy & Boch, supposedly high end and german.
They replaced the toilet seats the first time (2 bathrooms so 2 toilet seats) due to the yellowing issue, but not the second time (as it happened on the replacement ones too after 2 years).
I definitely wouldn't purchase there products. Awful service and products.

I remove the whole toilet seat once every couple of weeks, soak in the bath with cold water and a bit of bleach. Comes up like brand new.