Yes Andy.Could you be thinking of Sylglas tape?
Waterproofing Tape by Sylglas - a flexible self adhesive waterproofing tape designed for general sealing jobs in and around the home and garden suitable for rainwater gutters, down pipes, greenhouse glazing bars insulation lagging. Sylglas DIY sealing waterproofing safety products - Practical...www.sylglas.com
I sealed the leaking van roof and when the chaps that sold the vehical to me saw it the extracted the urine. Well they were coach builders but I was just a builder so what did they expect?