All weather sealant, even seals under water, Aquafix : Amazon.co.uk: DIY & Tools
Everbuild Plumbers Gold | Excellent Primerless Adhesion with Mould Shield Silicone Sealant - Can be Applied to Wet Surface and Under Water - Clear - 290 ml : Amazon.co.uk: DIY & Tools
All weather sealant, even seals under water, Aquafix : Amazon.co.uk: DIY & Tools