What Should Be Included in a Concealed Cistern OEM Specification Sheet?
Aug 19, 2026
What Should Be Included in a Concealed Cistern OEM Specification Sheet?
A Practical Guide for Importers Before Mass Production
A good concealed cistern OEM specification sheet should define more than the tank size and flush volume. It should clearly identify the tank construction, critical dimensions, flushing system, water-pressure conditions, installation interfaces, service access, QC requirements, packaging, spare parts, and approved component configuration.
For importers, the purpose of the specification sheet is simple:
Everyone involved in the project should know exactly what has been approved before mass production begins.
This becomes especially important when a product is customized for a specific market or private-label brand. A missing dimension or unspecified component can become a production change, installation problem, or after-sales issue later.
1. A Specification Sheet Is More Than a Product Datasheet
A catalogue datasheet usually tells buyers what a product is.
An OEM specification sheet needs to define what the factory is actually required to produce.
That difference matters.
A standard product page might say:
Concealed cistern
Plastic tank
Dual flush
3/6 L
Front actuation
An OEM specification should go further.
It may need to identify:
Exact tank material
Product dimensions
Water connection position
Outlet configuration
Flush valve model
Inlet valve model
Flush-volume settings
Actuation method
Service-opening requirements
Packaging
Approved accessories
Inspection requirements
The more customized the project, the more important this distinction becomes.
2. Start With the Tank and Critical Dimensions
The first section should identify the physical product.
At minimum, define:
| Item | What to specify |
|---|---|
| Tank material | Exact material or approved material grade |
| Overall dimensions | Length × width × height |
| Installation depth | Minimum / fixed / adjustable |
| Water capacity | Nominal capacity if relevant |
| Inlet position | Top, rear, side, etc. |
| Outlet connection | Size and configuration |
| Actuation position | Front, top or other |
| Service opening | Location and usable dimensions |
| Insulation | Whether included and its specification |
Do not assume that a dimension shown on a drawing is automatically a production-critical dimension.
Some dimensions affect only appearance.
Others determine whether the product will physically fit into the intended installation.
Market insight
A specification sheet should identify which dimensions are critical to function and installation.
This is particularly important when the same tank will be supplied to different cabinet, frame or project configurations.
Actual manufacturer documentation commonly separates dimensions, connection positions, service access and installation conditions rather than treating the tank as a simple rectangular container.
3. Define the Flush System as a Complete Configuration
Do not write only:
Dual flush: 3/6 L
That is not enough for an OEM project.
The specification should identify the complete flushing configuration:
Flush valve
Inlet valve
Full flush volume
Reduced flush volume
Adjustment range
Actuation method
Flush plate or button
Overflow arrangement
Relevant connections
For example, a manufacturer may offer a factory setting of 4.8/3 L while allowing the large flush to be adjusted to 4.5, 6 or 7.5 L and the small flush to 3–4 L.
That is much more useful information than simply writing "dual flush."
Why this matters
Two products both described as "3/6 L dual flush" may still use different valves, actuators and adjustment mechanisms.
The specification sheet should therefore freeze the approved system configuration, not merely the headline flush volume.
For a deeper explanation of how these components should be evaluated together, see [how the flush system should be configured as a complete system].
4. Specify Water-Pressure Conditions
Water pressure should have its own section.
Include:
Minimum operating pressure
Recommended operating range
Maximum pressure where applicable
Reference pressure for flow-rate data
Water temperature limits if relevant
This prevents a common mistake:
treating the pressure range of the tank as if it were automatically the pressure requirement of every internal component.
For example, one Geberit concealed cistern specifies a flow-pressure range of 0.1–10 bar and also provides flow-rate data at 3 bar.
Those are different pieces of information.
If the target market has unusually low, high, or fluctuating water pressure, that condition should be included in the OEM specification rather than discussed informally by email.
5. Installation Interfaces Need to Be Explicit
Installation-related specifications are often where small omissions become expensive.
The specification should identify the interfaces that installers actually depend on.
Depending on the product, this can include:
Water inlet thread
Inlet location
Outlet diameter
Flush-pipe dimensions
Fixing points
Mounting brackets
Actuator opening
Service opening
Adjustable components
Connection accessories
Market insight
"The tank fits" is not the same as "the installation interface fits."
For OEM projects, the interfaces should be frozen before mass production.
6. Define Service Access Before You Approve the Design
A specification sheet should not only describe how the product is installed.
It should also define how it will be serviced.
Ask:
Which components can be accessed through the service opening?
And:
Can the main valves be removed without dismantling the finished installation?
This is an important long-term consideration.
For a high-volume project, serviceability can affect the total cost of ownership long after the original purchase.
A specification sheet can therefore include:
Service-opening dimensions
Accessible components
Required removal clearance
Replacement procedure reference
Spare-part identification
7. Freeze the Critical Components
This is one of the most important sections for an OEM project.
A buyer may specify the external product accurately but leave the internal components open.
That creates room for unapproved substitutions.
The specification should identify the components that cannot be changed without approval.
For example:
Critical components
Flush valve
Inlet valve
Actuator
Pneumatic mechanism
Flush plate
Sealing components
Water connection components
Approved alternatives
If alternatives are permitted, list them explicitly.
For example:
Approved valve A or approved valve B, subject to functional validation.
This is much safer than:
"Equivalent component acceptable."
The word equivalent can mean very different things to different parties.
8. Component Substitution Should Trigger a Review
A good OEM specification should also define what happens when a component becomes unavailable.
Suppose the approved production configuration is:
Tank A + Flush Valve A + Inlet Valve A + Actuator A
The supplier later proposes:
Tank A + Flush Valve B + Inlet Valve A + Actuator A
The replacement may appear dimensionally compatible.
But the change could affect:
Flush volume
Discharge rate
Actuation force
Sealing
Installation
Maintenance
Ceramic compatibility
Therefore, the specification should state:
No critical component substitution without buyer approval and required revalidation.
This is particularly important for long-term OEM programs.
9. Define QC Requirements in the Specification
A product specification should tell the factory what the product should be.
The QC section should define how conformity will be checked.
Depending on the project, this can include:
Functional inspection
Flush operation
Inlet valve operation
Button/actuator operation
Adjustment function
Water-related inspection
Leakage
Filling
Overflow
Sealing
Dimensional inspection
Critical dimensions
Connection positions
Installation interfaces
Appearance inspection
Surface defects
Scratches
Deformation
Colour consistency
Packaging inspection
Product protection
Accessories
Labels
Carton condition
The exact inspection method and sampling level should be agreed before production.
For example, some manufacturers publish dedicated installation and maintenance documentation alongside their product specifications, which helps define the expected configuration and service procedures.
For more detail on one of the most important pre-shipment checks, see our article on how concealed cisterns are leak tested before shipment.
10. Don't Leave Packaging Until the End
Packaging should be part of the approved specification, especially for export orders.
Specify:
Individual packaging
Carton dimensions
Protective materials
Accessory packaging
Product identification
Quantity per carton
Pallet requirements where applicable
Shipping marks
The objective is not simply to make the package look professional.
The packaging needs to protect:
Tank body
Valves
Flush connections
Flush plate
Small fittings
Installation accessories
For example, current manufacturer documentation may define not only the cistern but also the included flush bend, fixing brackets, connection components and protection box.
If accessories are part of the customer's installation, they should be treated as part of the delivery specification rather than informal extras.
11. Add a Spare-Parts List
For a long-term OEM project, the specification sheet should identify the components that may need replacement.
A practical spare-parts list might include:
| Component | Part identification | Replacement status |
| Flush valve | Model / code | Replaceable |
| Inlet valve | Model / code | Replaceable |
| Seal | Part number | Replaceable |
| Actuator | Model / code | Replaceable |
| Pneumatic hose | Specification | Replaceable |
| Flush plate | Model / code | Replaceable |
The goal is to avoid a situation where a customer has a problem several years later and nobody knows exactly which component was used in the original production batch.
Some major manufacturers explicitly emphasize long-term spare-parts availability and backward compatibility as part of their concealed-cistern systems.
For an OEM buyer, this is a useful reminder:
The product specification should survive longer than the original purchase order.
12. Revision Control Is Essential for OEM Projects
This is one of the most overlooked areas in international manufacturing.
Suppose the buyer approves:
Specification Rev. A
The sample is then modified:
New flush plate
Different valve
Revised connection
New packaging
But the factory's purchasing department still has Rev. A.
Now two versions of the same product may exist inside the supply chain.
A simple revision-control system can prevent this.
For example:
Rev. A - Initial specification
↓
Rev. B - Sample modification
↓
Rev. C - Final approved specification
↓
Mass production
The final production version should be clearly identified.
The buyer and factory should also know:
What changed
When it changed
Who approved it
Which production batch uses the new version
Market insight
Version control is not paperwork for its own sake. It is a way to prevent an approved sample from becoming a different mass-produced product.
13. Include the Documents That Belong to the Product
Depending on the target market and project, the technical file may need to include more than the specification sheet.
Possible documents include:
Product drawing
Installation instructions
Maintenance instructions
Test reports
Declaration or certification documents where applicable
Material information
Spare-parts list
Packaging specification
QC inspection standard
Do not automatically assume that every market requires the same documents.
The documentation should be determined by the target market, applicable requirements and customer specification.
This also makes it easier for the importer to maintain a complete technical record for future orders.
14. A Practical OEM Specification Checklist
Before approving a concealed cistern for mass production, make sure the specification answers these questions:
Product
What is the exact tank material?
What are the overall and critical dimensions?
What is the installation depth?
Where are the inlet and outlet connections?
Flush system
Which flush valve is approved?
Which inlet valve is approved?
What are the full and reduced flush volumes?
What adjustment range is allowed?
What actuation system is used?
Operating conditions
What is the minimum pressure?
What is the recommended pressure range?
What test conditions are used?
Is the system suitable for the target market?
Installation and service
Where is the service opening?
Which components can be replaced through it?
What connection accessories are included?
What installation dimensions are critical?
Quality
What tests are required?
What are the acceptance criteria?
Which dimensions are inspected?
What sampling level applies?
Supply
What packaging is approved?
Which spare parts are required?
Which components cannot be substituted?
What revision of the specification controls production?
If these questions cannot be answered clearly, the product is probably not fully specified yet.
What Should a Supplier Be Able to Provide?
A professional OEM supplier should be able to turn the buyer's requirements into a controlled technical package.
At minimum, the buyer should expect to review:
Product specification
Technical drawing
Component configuration
Installation information
QC requirements
Packaging specification
Approved sample
Revision record
This creates a much stronger basis for mass production than relying on a quotation, product photograph and a few email confirmations.
Final Takeaway
A concealed cistern OEM specification sheet should do one thing exceptionally well:
Remove ambiguity before production begins.
It should define not only what the tank looks like, but also how it works, what components it uses, where it connects, how it is serviced, how it is inspected, how it is packed, and which version the factory is authorized to produce.
The most important information to freeze before mass production includes:
Critical dimensions
Flush configuration
Water-pressure conditions
Installation interfaces
Service access
Approved components
QC requirements
Packaging
Spare parts
Revision control
For importers, this level of specification can prevent a common OEM problem: a product that was technically "approved" but was never actually defined in enough detail to guarantee consistent production.
The specification sheet is therefore not just a technical document.
It is the reference point that connects the buyer, engineer, purchasing team, QC department and factory floor.
Preparing an OEM Concealed Cistern Project?
Before requesting a production quotation, prepare the target market, required dimensions, flush configuration, water-pressure conditions, installation interfaces and branding requirements.
A complete technical specification allows the factory to identify compatibility issues earlier, confirm the correct component configuration and establish the inspection requirements before mass production begins.
