We recommend using only silicone grease on O-rings. You must not use any petroleum containing product, which includes petroleum jelly (sometimes called “petrolatum”). A commercial product is Vaseline . We repeat: Do not use Vaseline , petrolatum or petroleum jelly on O-rings, for it will damage them. One acceptable product for use on O-rings is “Silicone Lubricant” in the catalog at http://www.tryphon.it/catalogo.htm. The catalog description says “Special silicone lubricant with PTFE”, and it is fairly inexpensive.Another acceptable product for use on O-rings is Gunk Plumber’s Silicone Grease. The Gunk part number is GR2V. You can find more information about this product at http://www.gunk.ca/prodsht-en/gr2.pdf (link will open in a new window). We found Gunk Plumber’s Silicone Grease in local hardware stores and the plumbing department of home improvement companies (such as Lowes and Home Depot). It may also be available at plumbing supply companies and auto part dealers.