Saw this just at the right time as installing a bath, and never had anything fail using this stuff, priced £7.39 @ screwfix!!
It's your 3 in 1 sealant.....
Sikaflex®-EBT+ is a multi-purpose one part, elastic, polyurethane adhesive and sealant. It bonds to all common building materials, is permanently elastic and has excellent grab and gap filling properties making it ideal for use in a wide range of building and maintenance situations.
Good weathering with high performance
Bonds to concrete, brick, mortar, wood, metals, glass, resins and plastics
Internal and external