For connecting 76mm and 102mm Vulcathene stacks to underground drainage systems of other materials where a flange connection is not available. Flexible adaptor couplings have a stepped moulded nitrile sleeve with different diameters at each end to enable pipes of differing outside diameters to be jointed economically and quickly without the use of bushes. The sleeve is fitted with two stainless steel clamping bands by which they are secured to the pipe ends.