Plumbing & technical: Toilet waste

Toilet drainage is one of the most critical aspects of a plumbing installation.
A toilet can be new, stylish, a major brand…
👉 if the drainage is poorly designed, problems will arise sooner or later.

In renovation, the constraints are even more numerous:
available height, old network, existing drainage type, accessibility standards…

Here's what you absolutely must check before choosing or relocating a toilet.

🚽 1️⃣ Drainage diameter: a non-negotiable basic

For a toilet:
👉 Ø100 mm (Ø110 mm outer)

❌ Frequent problems:

• Diameter reduction on an old installation
• "Jury-rigged" adaptation
• Undersized old networks

👉 A poorly sized toilet will always function poorly, even with a good slope.

📐 2️⃣ The slope: essential, but controlled

👉 Recommended slope: 2 to 3 cm per meter

• ❌ Too shallow → stagnation of waste
• ❌ Too steep → water flows without carrying solids

👉 This is the #1 cause of drain rework in renovation.

📏 3️⃣ Drainage height: an often-forgotten constraint

The height of the drainage outlet depends on:

• The type of toilet
• The finished floor level
• The standards to be met

🔹 Standard toilet

• Tolerant standard height
• Easier adaptation

🔹 Accessible toilet (for disabled persons)

• Regulated seat height
• Strong constraints on the drainage outlet
• Little margin for error

👉 Incorrect height =

• ❌ Poor connection
• ❌ Stress on the flush pipe
• ❌ Premature wear
• ❌ Possible leaks

🔧 4️⃣ The toilet flush pipe: a key element too often overlooked

The toilet flush pipe is essential for watertightness and proper flow.

❌ What I often see:

• Old flush pipes
• Hardened seals
• Invisible cracks
• Deformed fittings

👉 A worn-out flush pipe must be systematically replaced during a renovation or toilet relocation.

It's a small cost… that avoids big problems.

🧱 5️⃣ The type of drainage: floor or wall (vertical or horizontal)

The choice of toilet directly depends on the existing drainage.

🔹 Floor drainage (vertical)

• Often found in old installations
• Little freedom of movement
• Specific toilets required

🔹 Wall drainage (horizontal)

• More common today
• More flexible
• Strongly depends on height and slope

👉 You don't choose a toilet at random:
the installation dictates the model, not the other way around.

🧱 6️⃣ Age of installation: a determining factor

In renovation:

• Networks are sometimes old
• Standards have evolved
• Materials too

❌ Classic mistake:
Adapting a modern toilet to an old installation without prior study.

👉 Result:

• Invisible constraints
• Costly rework
• Mediocre performance

✅ The right approach (the one I recommend)

Before any purchase or modification:

1. Analyze the existing drainage
2. Check the actual slope
3. Control the available height
4. Inspect the flush pipe
5. Choose the toilet based on the installation
6. Anticipate accessibility constraints if necessary

👉 This upstream work guarantees:

• ✓ A reliable installation
• ✓ Less after-sales service
• ✓ Lasting comfort