Messaged for visitors

I think that is fine as long as the tone is direct and up front. e.g. Our plumbing can't cope with panty liners, wipes etc. Please can you use the bin.
I can't stand notices that are overly polite and somehow slightly cutting e.g. "we would be obliged if guests would consider others...

I think that is fine. Make sure there is a bin too.

I've had a "NO PLASTIC down the loo" (bit more detail than that but that's the essential message) sign up for ages. You can't miss it when you're sitting on the loo as it's positioned right in front of you. We are not connected to the public sewer but have a natural soakaway that has worked for over 120 years. Don't want to foul it up with stuff that won't biodegrade easily. Nothing like making people face up to the difficult realities of plastic disposal, is there?!

How about a 'holier than though' sign :This is a green household, please only flush loo paper!

Actually, mine is a bit like that, with a reference to the rule in yachts: "don't flush anything that hasn't been through you first! Loo paper is the exception."

Baggy I had that on my loo at our wee hoose up north as we had a septic tank - it mainly worked.........

Thanks everyone - glad I am not being unreasonable. I think I will change it to be similarly to Bagitha's 2nd suggestion because that made DH laugh!