Introduction

Lead/brass drain repair is one of those jobs that looks simple until you open a cupboard and find a 1930s lead waste married to a modern brass trap. Leaks, green corrosion, wobbly slip nuts—sound familiar? In this guide, we’ll cover what the issues are, why lead and brass behave the way they do, and how you can repair or replace sections quickly and safely. You’ll get practical steps, real-world measurements, and work-ready checklists you can use on your next call-out.

Quick Answer: Lead/brass drain repair usually means replacing leaking brass traps with new tubular brass or plastic, and coupling lead waste to modern pipe using shielded rubber couplings. Focus on safe lead handling, correct trap seal depth (50–75 mm), proper fall (6–10 mm per 300 mm), and watertight compression joints.

Table of Contents

• Quick Answer
• Key Takeaways
• Diagnose Lead/Brass Drain Failures
• Safety And Compliance For Lead Work
• Repair Options: Replace, Couple, Or Rebuild
• Step-By-Step: Brass Trap Replacement
• Step-By-Step: Lead Waste Section Replacement
• Testing, Sign-Off, And Warranty
• FAQ
• Conclusion

Key Takeaways

• Set correct fall: 6–10 mm per 300 mm of horizontal waste run to prevent standing water and smells.
• Trap seal matters: keep a 50–75 mm water seal (typical: 75 mm for basins/sinks, 50 mm for baths/showers).
• Use shielded couplings to join lead to 32 mm, 38 mm, 40 mm, or 50 mm modern pipe without heat.
• Hand-tighten compression nuts, then a further quarter turn; wrap PTFE 10–12 mm tape 3–4 times on threaded tails.
• For lead, follow Control of Lead at Work guidance; wet methods, gloves, and clean-up reduce exposure risk.

Diagnose Lead/Brass Drain Failures

What Goes Wrong

• Worn or mis-seated washers on brass tubular traps (common around slip nuts and the union at the wall).
• Corroded brass threads or de-zincification causing pinholes and green staining.
• Distorted lead waste entering the wall or floor—ovalised or cracked from years of movement.
• Poor falls: trap arms running flat or back-graded; water sits and creeps past joints.

Quick Checks

• Run water for 2–3 minutes; use a dry tissue at each joint to spot drips instantly.
• Check trap seal depth with a tape—should be 50–75 mm depending on the fixture.
• Confirm pipe diameters: basins often 32 mm or 1 1/4 in; kitchen sinks and baths commonly 40 mm or 1 1/2 in; some older brass may be 38 mm.
• Inspect for heat-damaged lead (dull, oxidised) and unsupported spans greater than 450 mm.

Example

A 1940s lead waste under a basin with a 32 mm brass bottle trap. You find a drip at the wall union and a flat trap arm. The fix: new 32 mm brass trap, 6–10 mm per 300 mm fall, and a 32 mm-to-lead shielded coupling at the wall.

Safety And Compliance For Lead Work

Lead Handling Basics

• Follow the UK’s Control of Lead at Work guidance: minimise dust, avoid heat on old lead, wash hands before eating, and keep work areas clean.
• PPE: nitrile gloves, eye protection, and a P2/P3 mask if you might create dust when cutting or scraping oxides.
• Use wet methods: damp rags and a spray bottle to keep swarf and dust down when cutting lead.
• Segregate waste: double-bag rags, wipes, and offcuts; dispose according to local rules.

When To Refuse Or Upgrade

• Badly cracked or crushed lead over long runs: replacement is safer than patching.
• Historic wiped joints within a void near timbers: avoid heating; use no-heat couplings and replace back to sound material.
• Unvented long trap arms or drum traps: modernise to reduce future callbacks.

Repair Options: Replace, Couple, Or Rebuild

You have three main routes. Pick what’s safest, fastest, and most durable for the situation.

Pro tip: Most residential call-outs combine the first two—new trap plus a lead-to-40 mm coupling at the wall or floor.

Step-By-Step: Brass Trap Replacement

Tools And Materials

• Adjustable or slip-joint pliers; strap wrench for polished brass
• New 32 mm or 40 mm brass or plastic trap with washers
• PTFE tape (10–12 mm wide)
• Silicone grease for washers
• Level and tape measure

Steps

1. Isolate and protect: Place a tray and towels. Remove the old trap—support the trap while loosening slip nuts to avoid twisting the wall pipe.
2. Clean mating faces: Remove old fibre/rubber washers and limescale; wipe seats smooth.
3. Dry fit: Assemble loosely. Check trap seal depth (target 75 mm on basins/sinks). Confirm fall on the trap arm: 6–10 mm per 300 mm towards the drain.
4. Seal threads: On threaded tails (e.g., basin waste tail to trap), wrap PTFE 3–4 turns clockwise. Lightly grease compression washers.
5. Tighten correctly: Hand-tight first, then a quarter turn with pliers. Don’t over-crush washers; watch for even seating.
6. Test: Fill the basin and release. Check each joint with a tissue. Re-check after 5–10 minutes to catch slow weeps.

Outcome

A properly aligned trap with the correct fall eliminates most slow weeps and odours. Expect 30–60 minutes on straightforward swaps.

Step-By-Step: Lead Waste Section Replacement

Replacing a short lead stub-out or bridging to modern pipe without heat.

Tools And Materials

• Fine-tooth hacksaw (24–32 TPI) or multi-tool with metal blade
• Shielded rubber coupling sized for lead OD to 32/38/40/50 mm modern pipe
• Short length of 40 mm solvent-weld or compression pipe and fittings
• Emery cloth, damp rags, marker, tape
• Level, support clips (every 300–450 mm)

Steps

1. Assess the lead: Find sound lead—no splits or deep pitting. Aim to cut back to a straight section at least 40–60 mm from any old wiped joint.
2. Cut and true: Use a fine-tooth saw for a square cut. Deburr gently. Wipe with a damp cloth to control dust.
3. Size the coupling: Many older wastes are near 38 mm. Select a shielded coupling that lists lead-to-40 mm or the exact OD range.
4. Fit the coupling: Slide onto lead first. Insert the 40 mm pipe into the other side. Tighten bands evenly. Follow the manufacturer’s torque guidance—snug until rubber compresses uniformly.
5. Rebuild the run: Keep the new horizontal section with 6–10 mm fall per 300 mm. Clip at 300–450 mm intervals to prevent movement.
6. Connect the trap: Use a 40 mm or 32 mm trap as needed with an adapter. Ensure a 50–75 mm water seal.
7. Test thoroughly: Fill-and-dump twice. Tissue-check joints and feel for movement.

Example

Under a bath, the lead stub is oval and only 35 mm long. You cut back 60 mm, true the end, use a lead-to-40 mm shielded coupling, then run 400 mm of 40 mm solvent-weld with correct fall. A new 40 mm tubular trap completes the repair.

Testing, Sign-Off, And Warranty

Water Test Routine

• Static test: Fill the fixture fully; hold for 2 minutes; check all joints.
• Dynamic test: Release; observe every joint for 60 seconds. Repeat once.
• Odour check: After 15 minutes, confirm no smells—trap seal intact.

Documentation That Protects You

• Photos: Before, during, after—especially of the lead condition and coupling sizes.
• Notes: Diameters used (32 mm/40 mm), fall achieved (e.g., 8 mm per 300 mm), products fitted.
• Warranty terms: Commonly 12 months on workmanship for drains; exclude customer misuse and chemical damage.

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FAQ

Is It Legal To Repair Lead Drains Or Must I Replace Them?

In most domestic settings, you can repair existing lead waste pipes if the work is done safely and you minimise exposure in line with Control of Lead at Work guidance. However, replacing deteriorated lead with modern pipework is usually recommended for reliability. For listed buildings or heritage restrictions, consult local requirements before altering original fabric.

Can I Connect Plastic To Lead Or Brass Drains?

Yes. Use a correctly sized shielded rubber coupling to bridge lead to 32 mm, 38 mm, 40 mm, or 50 mm plastic. For brass traps to plastic pipe, use compression or trap adapters. Avoid heat on old lead; no-heat couplings provide a durable, serviceable joint when installed on clean, round pipe.

How Do I Stop A Leaking Brass Trap Without Replacing It?

Check washer condition and seating first. Clean the mating faces, lightly grease new washers, and reassemble. Hand-tighten and add a quarter turn. Wrap threaded tails with 3–4 turns of PTFE. If threads are pitted or the body is out-of-round, replacement of the trap is usually faster and more reliable.

What Fall Should A Waste Pipe Have?

Aim for 6–10 mm of fall per 300 mm of horizontal run. Less than 6 mm can leave solids and soap scum behind; more than 10 mm can let water outrun solids in longer runs. Use a level and shims to set the gradient before final tightening and clipping.

Do I Need Specialist PPE For Lead/Brass Drain Repair?

Wear nitrile gloves and eye protection as standard. If you may generate dust or disturb oxides on lead, use a P2/P3 mask and wet methods to control dust. Wash hands before breaks and bag waste appropriately. Avoid heating old lead unless you’re trained and controls= are in place.

Conclusion

Lead/brass drain repair comes down to three things: safe handling, correct geometry, and reliable joints. Set a 50–75 mm trap seal, keep 6–10 mm per 300 mm fall, and use shielded couplings to transition lead to modern pipework. Most jobs wrap up in 45–90 minutes with a new trap and a clean lead-to-40 mm bridge. Want to get approvals faster? Use Donizo to dictate site notes, generate a branded proposal, send for e-signature, and convert to an invoice once signed. Try the free Discover plan to streamline your next call-out, or step up to Ascension for custom branding and payment tracking.