What makes 唐樓 drains different from modern flats?

Tong lau (pre-war or early post-war low-rise buildings, typically 4-6 storeys without lifts) share a single vertical cast-iron waste stack across all floors. A blockage anywhere in that stack affects units below it. Ground-floor units are worst affected because all waste passes through their connection point.

Who is responsible — my neighbour upstairs or me?

If the blockage is in the shared stack (affecting multiple floors), it is a building-wide issue — the landlord or building manager should coordinate. If it is inside your unit's branch (only your sink/toilet is slow), it is your responsibility. We can identify the location during diagnostic.

Can old cast-iron pipes be augered safely?

Yes, with care. Our technicians use flexible micro-sonic heads on older cast-iron to avoid cracking corroded joints. We always do a re-test before leaving to confirm flow is restored. If we find a cracked stack section, we will tell you — that is a plumbing repair, not an unblock.

Why does the ground-floor unit always get the worst of it?

Because every unit's waste passes through the ground-floor connection before entering the public sewer. A stack blockage at any level will cause backflow at the lowest connected point first. If you are on the ground floor of a tong lau and see slow drainage, call immediately — it often gets worse fast.

Is there anything I can try before calling?

If only your unit is affected: try pouring 2L boiling water slowly down the affected drain (not toilet — can crack ceramic). If it clears, it was likely grease. If it does not, or if multiple drains in your unit are slow at once, it is likely a stack issue — call us.

Tong Lau Drain Unblocking HK (唐樓) — From HKD 800

What makes 唐樓 drainage unique

Three structural realities that shape every tong lau call we run:

1. Single shared cast-iron waste stack

Modern flats have separate soil and waste stacks, often with PVC or uPVC pipes. Tong lau typically have one vertical cast-iron stack running from roof vent to ground-floor connection, serving every unit's toilet, kitchen and bathroom. A single blockage at any level affects all units below it — and the ground floor always gets hit first.

2. Corroded joints and narrowed internal diameter

After 50+ years, cast-iron stacks develop internal scale and joint corrosion that narrows the effective diameter. What was 100mm inside is now 60-70mm. This means hair, grease and wet-wipe clusters that would pass through a modern PVC stack get stuck here. The pipe is not blocked by abuse — it is blocked by age working against normal use.

3. Ground-floor trap — the canary in the stack

The ground-floor unit's connection to the public sewer is the lowest point in the stack. When a blockage forms above (usually between 1/F and 3/F), waste water finds the path of least resistance: straight down to the ground floor. Ground-floor residents in tong lau should call immediately on first signs of slow drainage — it rarely self-resolves.

Common 唐樓 drain problems

Stack blockage — multiple units slow (most common). If 2nd + ground floor are both slow, the blockage is in the shared stack. Needs coordinated access (usually via 1/F access point). We scope, confirm location, clear and re-test.

Ground-floor backflow. Wastewater from upper units enters your floor drain, toilet or kitchen sink. Call immediately — this is a health hazard and gets worse fast. We priority-dispatch for ground-floor backflow.

Corroded stack joint leak. Visible water stain on exterior wall at pipe joint height. This is a plumbing repair (not unblock) — we diagnose, you need a licensed plumber for the fix. We refer trusted partners.

1/F kitchen grease trap overflow. Many tong lau 1/F units still have the original under-sink grease trap. Over decades, it fills solid. Clearing it is a separate scope — we quote on-site.

Foreign object in toilet (any floor). Wet wipes, kid's toys, dental floss bundles — the usual. Auger clears from HKD 800 for in-unit access.

Roof vent blockage. The top of the stack vents through the roof. If blocked by leaves or debris, the whole stack drains slower. Access via roof (we coordinate with building).

When to call DrainFix vs. when to call someone else

Call us if: your toilet, kitchen, bathroom or floor drain inside the unit is blocked or draining slow. We diagnose first, confirm if it is your unit or the shared stack, and give a written quote on WhatsApp.

Coordinate with your building / neighbours if: multiple floors are affected. The shared stack is building infrastructure — if 3 units are slow, it is a building problem. We can still clear it but we need access from at least one intermediate floor.

Call Buildings Department if: there is a structural drain failure (cracked stack, collapsed section, UBW affecting drainage). Not our scope — we clear blockages, not replace pipes.

Call FEHD (食環署) if: the public sewer or roadside drain is blocked. Free government service for public infrastructure.

Tenant vs landlord — who pays in a 唐樓?

Tong lau often have no formal OC or management company. General HK norms (not legal advice):

Tenant: blockages caused by your use — hair, wet wipes, grease, foreign objects in your unit branch.
Landlord (owner): shared stack blockages affecting multiple floors, corroded pipe replacement, structural drain failure.
Split responsibility: if a neighbour's misuse caused the stack blockage that flooded your ground floor — document with photos before cleanup, we provide before/after evidence on WhatsApp.

See our tenant vs landlord guide for paste-ready WhatsApp templates and dispute-prevention photo evidence.

Pricing — starting HKD 800

Standard in-unit drain clear (toilet / kitchen / bathroom / floor drain) in a tong lau: from HKD 800. Includes diagnostic, mechanical clearing, full re-test before we leave, before/after WhatsApp photos.

Shared stack access requiring 2+ floors coordination: from HKD 1,200 (we clear from both access points and re-test the full stack).

CCTV inspection of cast-iron stack (if structural issue suspected): from HKD 1,500, quoted on-site.

No fixed-price guarantee. No 7-day re-block guarantee for shared stack (upstream neighbour can re-block). On-site re-test before we leave — that is the warranty we can stand behind. See full price list.

Frequently asked questions

What makes 唐樓 drains different from modern flats?: Tong lau share a single cast-iron vertical stack across all floors. A blockage anywhere affects units below. Ground-floor units are worst affected because all waste passes through their connection point.
Who is responsible — my neighbour upstairs or me?: If the blockage is in the shared stack (affecting multiple floors), it is a building-wide issue — the landlord or building manager should coordinate. If it is inside your unit branch (only your drain is slow), it is your responsibility. We can identify the location during diagnostic.
Can old cast-iron pipes be augered safely?: Yes, with care. Our technicians use flexible micro-sonic heads on older cast-iron to avoid cracking corroded joints. We always re-test before leaving. If we find a cracked stack section, we tell you — that needs a licensed plumber, not an unblock.
Why does the ground-floor unit always suffer?: Because every unit's waste passes through the ground-floor connection before entering the public sewer. A stack blockage at any level causes backflow at the lowest point first. If you are on the ground floor of a tong lau and see slow drainage, call immediately.
Is there anything I can try before calling?: If only your unit is affected: pour 2L boiling water slowly down the affected drain (not toilet). If it clears, it was likely grease. If not, or if multiple drains are slow at once, it is likely a stack issue — call us.

🏚️ Why 唐樓 (tong lau) drains block differently