Hi Brendan,
We received a few information from a TSIRC staff related to the materials of outlet pipe and end caps. He said it’s made of Hume-King floodgate (also known as reflux valve or tidal flap) moulded from fibreglass reinforced polyester, with high tensile 316 stainless steel built-in hinges, and replaceable neoprene sealing rings.
I hope this helps!
Regards,
Jean