Abstract: A combination quick-disconnect female fitting adaptable for snap coupling to a corresponding male fitting connected to a tap water faucet, is provided which permits all the required attachments to a reverse osmosis (RO) water purifier to be made with the single snap coupling of the female fitting to the male fitting. Installation of the entire RO water purification system can be reduced to mere screwing of the male fitting to a tap water faucet and snap coupling the combination female coupling thereto. Separate lines for concentrate and overflow purified water from the water purifier to the combination female fitting and tap water therefrom to the water purifier can be conveniently manifolded into a sidearm section of the female fitting. The fitting is particularly useful for small RO water purifiers. There is also provided a single mechanism for simultaneously securely fastening three pieces of tubing to a fitting containing three nipples adapted to receive tubing.