Technical guide · John Guest 12 mm, push-fit fittings, LLDPE tube, BSP threads and water circuits in mobile vehicles
Many motorhome, camper, caravan, motorhome and mobile vehicle users come to Install Beer looking for John Guest connectors to repair a leak, change a pump, connect a tap, adapt a heater, install an external inlet or redo part of the water circuit.
Although Install Beer mainly uses John Guest for beverage dispensing, water, filtration and technical systems, many sizes match those used in mobile vehicles: especially the 12 mm semi-rigid tube and the BSP threaded adapters.
Quick summary
In motorhomes, campers and caravans, the most common size for fresh water circuits is 12 mm outside diameter semi-rigid tubing. The most sought-after connectors are usually 12 mm straight coupler, 12 mm elbow, 12 mm tee, shut-off valve, non-return valve, plug, bulkhead fitting, locking clips, inserts, 12 mm to 1/2” BSP adapters and 12 mm blue, red or natural tube.
The key idea: measure the pipe from the outside, not the inside
In John Guest push-fit fittings, the tube size is identified by the outside diameter. If the tube is 12 mm, the fitting must be for a 12 mm outside diameter tube. It should not be confused with inches, BSP threads, or the hose’s inside diameter. This confusion is one of the most common causes of incorrect purchases when repairing campers and motorhomes.
Guide contents
John Guest connectors for motorhomes: what they are and what they’re used for
John Guest quick connectors are push-fit fittings designed to join tubes quickly, safely and removably in compatible applications. In a motorhome, camper or caravan they allow you to connect tube runs, create branches, adapt a pump, connect a tap, install a shut-off valve, run a line through a panel or repair a leak without resorting to traditional soldering, glues or hose clamps.
Their main advantage is that they make assembly and maintenance easier in confined spaces. In a campervan or motorhome it’s common to work inside cabinets, under sinks, near tanks, behind panels or in hard-to-reach areas. That’s why 12 mm push-fit fittings are especially useful for repairs, extensions and replacements.
Official John Guest distributor in Spain
Original product
We work with original John Guest connectors, fittings, tubes and accessories for technical applications.
Technical advice
We help identify size, thread, compatibility and type of part according to the installation point.
Real-world applications
Water, beverage, dispensing, water treatment, motorhomes, campers, caravans and mobile systems.
The key size: 12 mm OD tube
In push-fit connectors, the important dimension is the outside diameter of the tube. In many water installations for motorhomes, campers and caravans, 12 mm OD semi-rigid tubing is used, but this should not be taken for granted. You must measure the tube with callipers or an accurate ruler before buying.
12 mm outside
Common size in fresh water circuits for campers, caravans and motorhomes.
BSP threads
Very common on pumps, taps, filters, heaters, through-bulkhead fittings, and hydraulic accessories.
Do not confuse
12 mm and 1/2” should not be considered equivalent in push-fit connectors.
| Size | Where it appears | Usual use | What to order |
|---|---|---|---|
| 12 mm outside | Water circuits in campers, caravans, and motorhomes | Main line, branches, taps, tanks and repairs | John Guest fittings for 12 mm tubing |
| 1/2” BSP | Pumps, taps, filters, heaters and adapters | Connecting tube to threaded equipment | Compatible 12 mm x 1/2” BSP adapter |
| 3/8” BSP | Some taps, filters, pumps and compact accessories | Smaller-size connections | 12 mm x 3/8” BSP adapter if required |
Which John Guest fitting you need depending on the issue
Before choosing a specific fitting, it’s a good idea to start from the real use of the part. It’s not the same to repair a cut tube as it is to connect a pump, install an exterior tap, create a branch to a shower, or temporarily shut off a line.
| Need | Recommended part | Usual use |
|---|---|---|
| Repairing a cut tube or a leak | 12 mm straight connector | Join two sections of tubing with the same diameter |
| Change the direction of the tube | 12 mm elbow | Turns inside furniture, sinks, tanks or tight areas |
| Create a branch line | 12 mm tee | Run a line to a tap, shower, boiler or external point |
| Connect a pump, tap or threaded equipment | 12 mm x BSP thread adapter | Connect push-fit tube to male or female threads |
| Pass through a wall, panel or tank | John Guest bulkhead fittings | Neat routing of the water line |
| Shut off the water supply | 12 mm shut-off valve | Isolate an area for maintenance or repair |
| Prevent water backflow | 12 mm non-return valve | Protect pump, tank or sensitive lines |
| Temporarily shut off a line | 12 mm end plug | Close off an outlet during a repair or modification |
Where John Guest connectors are used in a camper
Pump area
Threaded adapters, shut-off valves, non-return valves, clips and inserts.
Sink and taps
Elbows, threaded adapters, shut-off valves and straight connectors.
Tanks
Bulkhead fittings, plugs, shut-off valves and outlet connectors.
Outdoor shower
Branch tee, elbows, shut-off valve and LLDPE tube.
Recommended John Guest kits for campers and travel
Besides buying individual parts, in a camper or motorhome it makes a lot of sense to prepare a small repair kit. A leak during a trip can put the water system out of action, and many issues can be solved with a few parts if you have the right spares with you.
| Recommended kit | What it should include | What it’s for |
|---|---|---|
| 12 mm repair kit | Straight couplers, elbows, tees, plugs, clips, inserts and tube cutters | Fixing leaks or breaks during a trip |
| Water pump kit | Threaded adapters, non-return valves, shut-off valve, tube and clips | Connect or replace a camper water pump |
| Tap or sink kit | Elbows, threaded adapters, tees, shut-off valve and tube | Install or renew the connection of an interior tap |
| Tank and bulkhead kit | Bulkhead fittings, adapters, plug, shut-off valve and tube | Create a neat outlet from the tank or panel |
Install Beer tip: if you travel frequently, always carry a small emergency kit with a straight coupler, elbow, tee, end plug, locking clips, inserts, tube cutter and a length of 12 mm tube. It takes up little space and can prevent an awkward breakdown during your trip.
How to correctly install a John Guest quick connector
Installation is simple, but it must be done carefully to avoid leaks. The tube must be clean, free of burrs and cut perfectly square. If the tube is oval, damaged, very soft or cut at an angle, the seal may not seat correctly.
- Cut the tube square using a suitable tube cutter.
- Make sure the end has no burrs, dirt or deformation.
- Push the tube all the way into the fitting.
- Pull gently outwards to verify that it is securely held.
- Fit a safety clip if the installation requires it or if there are vibrations.
- Pressurise the system and check that there are no leaks.
Common mistakes when buying fittings for a motorhome
When to ask for help before buying
If you’re unsure about the size, thread or type of connector, it’s best to check before placing your order. Send us a photo of the tube, the old fitting and the point where it is installed. With that information we can better advise you whether you need a straight connector, elbow, tee, threaded adapter, bulkhead fitting, shut-off valve, non-return valve, plug, insert or clip.
Frequently asked questions about John Guest connectors for campers
What tube size is normally used in motorhomes and campers?
In many fresh water installations for motorhomes, campers and caravans, 12 mm OD semi-rigid tubing is used. Even so, you should always measure the tube before buying.
Are John Guest 12 mm and 1/2” the same?
No. 12 mm and 1/2” should not be considered equivalent in push-fit connectors. The fitting must match the actual outside diameter of the tube.
Is Install Beer an official John Guest distributor in Spain?
Yes. Install Beer is an official John Guest distributor in Spain, selling quick connectors, fittings, tubes and accessories for water, beverage, dispensing, water treatment, motorhomes, campers and technical systems.
Can I use John Guest connectors with drinking water?
John Guest offers ranges for water and beverage applications, but you must always check the data sheet of the specific product. In drinking water circuits, use parts and tubes suitable for food contact or potable water.
Are they suitable for hot water?
It depends on the product, the tube and the working conditions. Before installing in a hot water line, boiler or heater, check the maximum temperature allowed for the fitting and for the tube used.
Which fitting do I need for a camper water pump?
You’ll normally need an adapter between 12 mm tube and the pump thread, which can vary depending on the model. It may also be advisable to install a shut-off valve and, in some cases, a non-return valve.
What do I do if I don’t know which part I need?
Send us a photo of the tube, the old fitting and the installation point. With that information we can help you identify whether you need a straight connector, elbow, tee, adapter, bulkhead fitting, valve, plug, clip or insert.
Technical notice: this guide is aimed at compatible water circuits. Do not use connectors without checking the technical data sheet in gas, fuel, brake, high-pressure, critical circuits or installations that require specific approval.