Reverse osmosis systems are plumbed in small bore plastic tubing with push fit connectors, and the great majority of leaks in these installations are caused by what was done to the tube rather than by any defect in the fitting. Understanding where the seal is actually made explains every rule that follows.
Where the seal is made
A push fit connector has two parts doing separate jobs. A stainless collet with angled teeth grips the outside of the tube and holds harder the more it is pulled. Behind it an O ring seals against the tube's outer surface. That is the crucial detail: the seal is on the outside wall of the tubing, so anything that scores, crushes or ovalizes that surface causes a leak, and pushing the tube in harder does not fix it.
Cutting and inserting
Cut square and clean with a proper tube cutter. Scissors, side cutters and knives crush the tube oval or leave a ragged edge, and an oval tube cannot seal against a round O ring. Cut back past any section that has been kinked, crushed or scratched rather than reusing it. Push the tube in until it stops, then keep pushing, because there is a second stage past the collet where it seats against an internal shoulder, and a tube stopped at the collet blows out under pressure.
Colour coding and layout
Kits usually supply different colours for the feed, permeate, tank and drain lines, and keeping to that scheme makes later diagnosis far easier, since the drain and permeate lines look identical in white. Photograph the arrangement before disconnecting anything during a service. Route tubing so it will not be crushed when the cabinet is filled or the appliance pushed back, leave gentle bends rather than tight ones, and support runs rather than letting them hang on connections.
Releasing, checking and locking
To release, depressurize first, then push the collet squarely into the fitting body while pulling the tube out. Pulling without pressing the collet damages the tube surface and guarantees a leak next time. Fittings can generally be reused; the tube end usually cannot, so cut back to fresh tube. Check every joint by hand after pressurizing and again an hour later, since these often weep only after pressure settles. Locking clips over the collet prevent accidental release. Our reverse osmosis guide covers commissioning.
Questions people ask about reverse osmosis fittings
Why do push fit connections leak?
The seal is made on the tube's outer surface, so a crushed, scratched or out of square cut prevents the O ring sealing.
How far in should the tube go?
Past the collet until it seats against the internal shoulder. A tube stopped at the collet blows out under pressure.
How do I release a fitting?
Depressurize, then press the collet squarely into the fitting body while pulling. Pulling alone scores the tube surface.
Can I reuse the tubing?
Usually not at the cut end. Cut back to clean undamaged tube before remaking the joint. Fittings themselves are reusable.