## Common ground
All options describe different materials used to make a toilet flush tank.
## Options at a glance
**3922.90 – Plastic**
- **Defining trait:** Made from synthetic polymer resin, typically lightweight and moldable.
- **Typical examples:** Injection-molded polypropylene or ABS tanks.
- **Best fit when:** The tank is lightweight, mass-produced, and used in residential or commercial fixtures.
**4016.99 – Rubber**
- **Defining trait:** Made from flexible, elastic natural or synthetic rubber; not typical for full flush tanks.
- **Typical examples:** Seals, gaskets, or flexible components inside a tank (not the main tank body).
- **Best fit when:** Referring to internal rubber parts like flapper valves or washers, not the tank itself.
**6910 – Ceramic**
- **Defining trait:** Fired clay-based material; traditionally used for high-end or vintage-style toilets.
- **Typical examples:** Classic porcelain tanks, often part of a one-piece toilet.
- **Best fit when:** The tank is solid, glazed ceramic, commonly found in older or premium models.
**7020.00 – Glass**
- **Defining trait:** Transparent or translucent material; extremely rare for flush tanks due to fragility and cost.
- **Typical examples:** Experimental or decorative toilet designs (e.g., art installations).
- **Best fit when:** The tank is fully visible, transparent, and used in artistic or niche applications.
## Key differences
| Feature | Plastic | Rubber | Ceramic | Glass |
|------------------|---------------|---------------|---------------|---------------|
| Material type | Synthetic polymer | Elastomer | Fired clay | Silicate |
| Durability | High | Low (wear) | Very high | Very low |
| Common use in tanks | Main body | Internal parts | Main body | Rare/none |
## How to choose
- Is the tank made of molded plastic? → 3922.90
- Is it a flexible seal or valve inside the tank? → 4016.99
- Is it solid, glazed ceramic (like porcelain)? → 6910
- Is it transparent and non-functional as a standard tank? → 7020.00
## Overlaps & pitfalls
- **Rubber** is not used for the main tank body—only internal parts. Confusing it with plastic or ceramic is common.
- **Glass** tanks are nearly nonexistent in real plumbing; likely a misclassification if claimed as a flush tank.
- **Plastic** and **ceramic** are both standard materials, but ceramic is heavier and more traditional. Choose based on material composition, not appearance.
- If the product is a full tank, **plastic (3922.90)** or **ceramic (6910)** are most likely correct. Use **rubber (4016.99)** only for seals, not the tank itself