Polyethylene tubing opaque 3/8" per metre, ref. A1OPAQUE38-TOURET

Polyethylene tubing 3/8" opaque, per metre

Flexible polyethylene tube, food-grade quality, outer diameter 3/8" (9.52 mm), supplied cut to length from reel. It provides the standard pressure connection for reverse osmosis units, under-sink filtration and water fountains: supply line, stage interconnection, reservoir outlet, line to tap.

Why 3/8" and not 1/4"

Diameter choice is not cosmetic; it affects flow rate:

• 1/4": the standard line on a domestic reverse osmosis unit. Supply, reject, short connections.
• 3/8": the high-flow section. Found on reservoir outlets, lines to tap when rapid filling is required, high-flow reverse osmosis units, water fountains and long runs where 1/4" pressure drop becomes significant.

On a long run or demanding draw point, switching to 3/8" is often the simplest way to gain flow without modifying the rest of the installation.

The opaque version: what changes

Clear tubing lets light through, and light combined with stagnant water eventually produces greenish deposits in exposed lines. Opaque tubing eliminates the problem at source. It is also more discreet when the line runs visibly, and it conceals the interior, avoiding customer calls over a simple reflection.

Accepted trade-off: water flow is no longer visible. On a point where you want to visually check flow or detect an empty line, clear tubing remains more practical.

Compatible with push-fit quick couplings

The tube fits into John Guest, DMfit and compatible instant-connection couplings: straight cut, insert fully until it bottoms out, the retaining clip grips and the O-ring ensures a seal. No glue, no tightening, no PTFE tape on the tube connection.

Note that 3/8" imperial and 10 mm metric are not interchangeable. The difference is small but enough for the O-ring not to seat correctly. Check your coupling brand and stay within the same system throughout the installation.

Cutting and assembly rules

Straight, clean cut. Use a tube cutter, never a knife or side cutters. An angled or crushed cut prevents the O-ring from seating around the full circumference: this is the leading cause of weeping under the sink.

Insert fully. The tube must pass the clip and bottom out in the coupling. A tube inserted halfway will hold dry and leak at the first pressure rise.

Pull to test. After insertion, pull gently on the tube. If it moves, it is not fully seated.

Large radius. Polyethylene bends but pinches in a tight angle, especially 3/8" which is stiffer than 1/4". Allow radius at coupling outlets and do not clamp the tube immediately behind a connection.

Mark your lines. On an opaque installation, circuits are no longer visually distinct. Marking or colour-coded clips save time on the next service call.

Sold per metre, cut from reel

Order the length you need for your job, without tying up a full reel. Allow margin: 50 cm extra is better than reworking a line for 10 cm short, and offcuts are always useful for testing or emergency repair.