One Hose, Two Outlets: Splitting a Line With a 3D-Printed T Connector

You've got one hose and two jobs. Maybe it's a raw-water thru-hull that already feeds the engine but now needs to share with a washdown pump, or a single deck-wash line you'd like to branch off toward a cockpit shower. Off-the-shelf plastic tees from the chandlery come in a handful of fixed sizes — 12 mm, 19 mm, 25 mm — and on an older boat, or one refitted more than once, the hose you're actually holding rarely matches any of them exactly.

This is one of the most common small annoyances in boat plumbing: not a broken part, just a missing size. Cutting into an existing line to add a branch means either hunting several chandleries for the right diameter, adapting with a stack of reducers that all leak a little, or living without the second outlet. None of those is a great option mid-project.

Why a printed T beats another trip to the chandlery

A parametric 3D-printed fitting sidesteps the sizing problem entirely: you set each of the three hose diameters to match what's actually on the boat — measured with calipers, not guessed from a size chart — and the file generates barbs sized to grip that exact hose. No adapters, no stacking reducers, no leaving one port loose because it's "close enough."

It also means you're not compromising the layout. A tee needs to sit where the branch actually has to go, at whatever angle the hose run allows; a printed part can be positioned and reprinted in minutes if the first attempt doesn't quite clear a bulkhead or stringer, which isn't true of a part you drove to the store for.

The part: a 3-Way T Hose Barb Connector

MarineLab3D's 3-Way T Hose Barb Connector is exactly what it sounds like: two in-line barbs plus a third, perpendicular branch, all on one cylindrical body sized automatically to the largest of the three ports.

Each of the three hose ports — call them A, B and C — is set independently between 6 and 60 mm inner diameter, so a mismatched setup (say, a 19 mm main line branching to a 12 mm accessory) is exactly as easy to configure as a matched one. Measure with calipers at the hose itself, not the fitting it currently sits on, since old hose softens and swells slightly with age.

What to measure before ordering

• Inner diameter of each of the three hoses that will connect (A, B, C) — measure at a fresh-cut end if you can.
• Available straight length either side of where the branch needs to sit, so the tee's body and the barbs' worth of hose overlap actually fit.
• Working pressure of the line — gravity-fed deck wash is very different from a pressurised washdown pump.

Material and print settings

The design is meant to be printed in PETG or PA12 (nylon), both of which handle the mix of dampness, occasional fuel or oil splash near an engine bay, and constant clamp pressure better than PLA. Print with supports — the T shape has overhangs from whichever direction you orient it — at 0.15–0.2 mm layers with 3 perimeters.

If the branch will run under any real pressure — above roughly 1 bar, which covers most washdown and deck-wash pumps — print in PETG rather than ASA (it seals better layer-to-layer), use solid walls rather than relying on infill to fill the wall thickness, set the Z-seam to a scarf joint, run a low part-cooling fan, and orient the part with the seam axis vertical. A generous wrap of PTFE tape on the hose-to-barb joint and stainless clamps on every port are still doing real work here — the print quality gets you a sound wall, the clamps and tape get you a sealed joint. Pressure-test the finished fitting at roughly twice its working pressure before it goes anywhere near a working system.

Installing it

Cut the existing hose cleanly where the branch needs to go, dry-fit the tee, and push each hose fully onto its barb — you should feel it seat past the first ridge. Two stainless hose clamps per port (offset slightly from each other) is the standard for anything below the waterline or under pressure; a single clamp is only acceptable on a gravity-drain or vent line that never sees pressure. Support the tee itself if it's hanging on the hose alone — a small zip-tied bracket or a printed pipe clamp nearby keeps the joint from working loose with engine vibration.

For splitting a line that already runs through threaded ports rather than plain hose — a pump inlet or a seacock, for example — you'll usually want a threaded transition first. Our BSP Hose Barb Fitting converts a BSP thread to a barb the T connector can grip, so the whole branch stays hose from that point on.

Related fittings worth knowing about

The T connector is one of a family of parametric barb fittings that all follow the same "measure your own hose" logic:

• Hose Barb Connector / Reducer (Barb–Barb) — for joining two hoses of different diameters in a straight run, no branch.
• Elbow Hose Barb Connector / Reducer — the same idea as the tee, but for a 90° turn instead of a branch.
• BSP Hose Barb Fitting — the bridge between a threaded port and plain hose.

If you need more than one extra outlet — say four or five branches off a single supply — a tee stops being the right tool; our BSP manifold guide covers the parametric manifold body designed for exactly that case. And if you're not sure how to measure hose and thread accurately before ordering any parametric fitting, that's covered step by step in our guide to measuring hose and thread for a 3D-printed fitting.

Browse the full range in the Plumbing & Pumps collection if you're outfitting more than one connection at once.

Safety note

3D-printed fittings are not certified marine equipment. Their strength and seal depend on your printer, material, settings and assembly, none of which we control from here — verify dimensions before printing, use a recommended material, inspect every print, and pressure-test before relying on it. Avoid using a printed fitting below the waterline or in any critical, life-safety or fuel/gas application unless it has been independently tested and, where relevant, certified for that use.

Questions about sizing a fitting for your setup, or about a branch configuration that doesn't quite fit this part? Email us at info@marinelab3d.com — we're happy to help you work out the right dimensions before you print.