You can either put this before the valve on the actual water line it's self, or do some creative plumbing in which case you will need to find compression to threaded T or compression to threaded female adaptor (you need to go to a plumbing supply house I doubt the box stores will have this but they do exist though most of the ones I have used are pvc threads to pvc compression fitting).
Yes they do make thread sealer in a plumbers tape version or you can buy the paste up to you. Plumbers tape and pipe dope are in fact made to seal threaded joints. {I said plumbers tape not the cheap junk teflon tape you find in the tool isle at your hardware store.}
To quote someone who took the time to type it out: (I'm just to lazy to get my code books out)
"Per ASTM (American Society of Testing & Materials) Standards we must use a thread sealant on all NPT (National Pipe Taper) Threads & fittings. The type of thread sealant is selected for compatibility with the material that the pipe will be conveying. In residential service the use of NPT joints is normally limited to water, natural gas, propane gas, #1 & #2 heating oils and occasionally low pressure steam, refrigerants or high-pressure air in a shop compressor system.
TEFLON TAPE:
When PTFE (Teflon) tape first became available they only made it in the common single density type, which we commonly find in the hardware and home supply stores. Later they began making a double density version, which was twice as thick. Many state and local codes then adopted the double density type as mandatory when making connections for natural gas however since both products were the same color (white) it was difficult for inspectors to be sure which product had been used. PTFE tape is now made in numerous varieties and they have issued a color standard to determine which type should be used.
WHITE-Single density- should only be used on NPT threads up to 3/8 inch.
YELLOW- Double Density- yellow double density is often labeled as "Gas type"
RED-Triple Density: (Note-the container is red but the tape itself appears as a pale pink color). Presently required on all joints ½" diameter or greater.
GREEN- Oil Free PTFE tape- Required for use on all lines conveying oxygen (I.E. –medical oxygen or welding oxygen lines).
COPPER COLOR- contains granules of copper and is to be used as a thread lubricant but is not approved as a thread sealant. (Generally it is used as a thread lubricant on bolts or pipe threads for mechanical applications where no physical seal is required.)
PTFE tape is only approved as a thread seal when applied correctly. To apply you begin at the end of the pipe and wrap the tape under tension in the direction of the thread turns. Each successive layer should overlap the previous layer by ½ to 2/3 and continue wrapping until the entire threaded portion of the pipe is covered. (Minimum of 3 full turns).
PIPE DOPE:
When looking for pipe dope in the hardware or home supply store we commonly find two types, a tube of dark gray paste labeled "Pipe dope" and tubes or small bottles of white "Teflon Pipe Dope". When selecting the pipe dope check the fine print very carefully to insure the product is listed as approved for the application you intend to use it for as some of these products have a very limited range of applications. As a rule the Teflon pipe dope will have the broadest range of applications and will normally meet all requirements that would typically be found in a residential environment.
WHICH TO USE?
Providing the Teflon tape or pipe dope is approved for the type of material you intend to convey in the pipe the choice of tape or dope is then a matter of personal preference. Although there is no hard and fast rule that I am aware of, as a rule most plumbers prefer to use pipe dope on all permanent pipe joints, which are pipe joints which would normally be expected to last the life of the structure whereas Teflon tape is often the material of choice when attaching the end use trim out items such as threaded angle stop valves or shower arms and shower heads or in any exposed location where pipe dope might prove unsightly."
