Why does my tong lau toilet keep blocking — 通完又塞?

In a tong lau, your toilet shares a cast-iron vertical stack with the units above and below. Recurrent blockages usually mean the shared stack — not your unit — has hardened rust scale narrowing the bore. Clearing your unit only buys 2-4 weeks. Diagnose the stack first via the access plate or CCTV; that is where the real fix is.

Who pays — me or the OC / 法團?

Under Cap 344 BMO, shared waste stacks are common-area infrastructure. The OC (業主立案法團) is responsible. Your tenant or owner share is limited to the lateral pipe inside your unit. We provide a written diagnostic and photo evidence that the OC can use to commission stack works. See bmo-cap-344-drain-specialist for details.

Does the OC have to use the building's listed contractor?

No. Cap 344 requires OCs to obtain competitive quotes for works above set thresholds. Owners can propose alternative contractors at the OC meeting. We can quote OC works against the incumbent — written, itemised, no on-site surprises.

Can you work in a tong lau without a lift?

Yes. Most pre-1970 Mong Kok, Sham Shui Po, Wan Chai tong lau are walk-up to floors 3-7. We carry hand-portable equipment (manual auger, hose-fed water flush) and we have stair-access surcharge disclosed up front (+HKD 100-200 floors 4+, +HKD 200-400 for floors 6+ depending on equipment needed).

Will you damage the original cast-iron stack?

No. We use mechanical auger and warm-water flush, never high-pressure jet on a stack older than 50 years (risk of fracture at corroded joints). If we suspect imminent stack failure, we tell you and the OC in writing — replacement, not clearing, is the answer.

Tong Lau Drain Unblocking HK (唐樓) — Shared Stack Specialist

What makes tong lau drainage unique

1. Shared vertical cast-iron stack

A typical pre-1980s tong lau has one 100mm vertical waste stack serving every unit on the column — your unit's toilet, the unit above, the unit below all dump into the same pipe. Fifty-plus years of HK humidity, salt air and detergent has built rust scale on the inner wall, reducing the effective bore to 60-70mm. When the bore narrows, blockages return faster and faster — what looks like "your toilet" is the building's stack. Clearing your lateral only buys weeks.

2. Cap 344 BMO compliance (shared infrastructure)

Under the Building Management Ordinance (Cap 344), the shared vertical stack is common-area infrastructure. The Owners' Corporation (業主立案法團) — or the manager if there is no OC — is responsible for its maintenance, not the individual owner. Your written diagnostic + photo evidence is what the OC needs to commission stack works. See our Cap 344 specialist page for the full compliance angle.

3. Original cast iron — no high-pressure jet

Modern PVC-stack buildings can take 4,000 psi hydro-jet without damage. Tong lau cast iron — especially at corroded joint collars — will fracture under high-pressure water. We never jet a tong lau stack older than 50 years. Mechanical auger and warm-water flush only.

Common tong lau drain problems

通完又塞 (recurring blockage). Cleared 6-12 weeks ago, back to slow drain. Shared-stack diagnosis needed. Lateral-only fix will not last.

Toilet gurgles when neighbour upstairs flushes. Classic stack-restriction symptom. Air gets pulled through your trap because the stack is partially blocked.

Floor drain backs up during heavy rain. Old combined-flow tong lau — stormwater and waste share the lower stack. Compounds during black rain.

Persistent sewage smell at floor trap. Vent stack capped, dry P-trap, or vermin in the dry portion of the stack. Diagnosis on-site.

Cracked cast-iron joint leaking into ceiling below. Not unblocking — repair work. We document for insurance + neighbour, refer to qualified plumber for replacement.

Subdivided unit (劏房) overload. Original 1960s stack designed for 1 toilet per floor, now serving 4-6 subdivided units. Failure inevitable. Owner/OC issue.

When to call DrainFix vs. when to call OC

Call us if: your unit's toilet, sink, floor drain is blocking, smelling, or backing up. We diagnose first — your lateral pipe vs the shared stack — and give you a written report.

If it is your lateral: we clear it from HKD 800. Re-test before leaving. Done.

If it is the shared stack: we give you written diagnostic + photos with date, location and recommended works. You take that to the OC or building manager. Cap 344 obliges them to act. Stack-clearing or partial replacement is OC-budget work, typically HKD 5,000-50,000+ depending on extent. We can quote OC works against the incumbent contractor — no obligation.

Call Buildings Department directly if: the OC refuses to act on documented shared-stack failure causing health hazard. They can issue a Repair Order under Cap 344.

Tenant vs landlord — who pays in a tong lau?

Tong lau ownership is fragmented; many are landlord-owned and tenant-rented. Norms (not legal advice):

Tenant: blockages in lateral pipes within the unit caused by use (hair, wipes, foreign objects, cooking grease).
Landlord: blockages in lateral pipes from old age (scale, corrosion); first call after move-in (usually pre-existing).
OC (法團) / all owners collectively: the shared vertical stack. Tenants do not pay; their landlord pays the OC levy that funds stack works.

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

Pricing — starting HKD 800, floor surcharge disclosed

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

Walk-up floor access surcharge (no lift): floors 4-5 +HKD 100; floors 6-7 +HKD 200-300 depending on equipment; floors 8+ quoted on-site. Always disclosed in writing before dispatch.

Written OC diagnostic report (for stack-suspected cases): HKD 0 add-on with a paid in-unit job. Standalone written diagnostic without clearing: HKD 500.

Shared-stack works (OC commission): scoped separately, typically HKD 5,000-50,000+, multiple-quote process. We are happy to quote against the incumbent.

No fixed-price guarantee. No 7-day re-block guarantee. On-site re-test before we leave is the warranty. See full price list.

How we work in a tong lau

Method (typical tong lau) Identify access point (toilet, kitchen sink, or stack access plate) → manual auger inspection of lateral → if lateral is clear and blockage is upstream, scope the shared stack → mechanical auger if cleared in-unit; if stack-restricted, written diagnostic for OC. Warm-water flush, never high-pressure jet on cast iron. Full re-test before leaving.

Frequently asked questions

Why does my tong lau toilet keep blocking?: Shared cast-iron stack with rust scale narrowing the bore. Clearing only your lateral buys 2-4 weeks. Stack diagnosis is the real fix.
Who pays — me or the OC?: Lateral inside unit: you (or landlord). Shared vertical stack: OC under Cap 344. We provide written evidence to support OC commissioning.
Does the OC have to use the building's listed contractor?: No — Cap 344 requires competitive quotes. Owners can propose alternative contractors at OC meetings.
Can you reach a tong lau without a lift?: Yes. Floor surcharge disclosed in writing before dispatch.
Will high-pressure jet damage the cast iron?: Risk of fracture at corroded joints. We do not jet stacks 50+ years old. Mechanical auger + warm water only.

🏚 Why tong lau (唐樓) drains block differently