Henward-- I am a retired Envirnmental Health Officer, Plumbing and Drainage Inspector, Building Inspector etc. I am telling you that they are giving you bad advice. Silicone (RTV) will not glue PVC. You must use PVC glue. It is used in all PVC installing in waste pipes, stormwater and cold water supply pipes throughout the world. It is available from all hardware stores. Tell them you want adhesive for PVC used in cold water supply reticulation. It is probably used in the cold water system in your house, it is in mine.