Intro

On many bathroom refits, the toughest part is getting a low pan pipe install right. A low pan (low-profile shower tray) needs tight pipework, correct falls, and a proper trap, all in a shallow build-up. In this guide, we show you exactly how to plan, set gradients, choose sizes, and test. You’ll see simple numbers, clear steps, and common fixes. Follow this and your low pan will drain fast, seal tight, and pass inspection first time.

Quick Answer

A good low pan pipe install uses a 40 mm waste with a 75 mm water-seal trap, set at a 1:40 fall (about 25 mm per metre) to the stack. Keep runs short, vent properly, pressure test supplies for 10 minutes, and flood test the tray with 20 mm of water for at least 15 minutes before sealing.

Table of Contents

• Key Takeaways
• Planning and Codes
• Tools and Materials
• Step-by-Step Low Pan Pipe Install
• Waterproofing, Testing, and Handover
• Common Mistakes and Fast Fixes
• Pricing, Variations, and Documentation
• FAQ
• Conclusion

Key Takeaways

• Use 40 mm waste and a 75 mm trap for most low pans.
• Set a 1:40 fall (≈25 mm per metre) on the waste run.
• Pressure test supplies for 10 minutes; flood test tray for 15 minutes.
• Allow 24 hours cure time for silicone around the pan.
• Plan for runs under 3 m before venting to avoid slow drainage.

Planning and Codes

A clean low pan pipe install starts with planning. Measure the tray outlet centre, trap height, and the route to the stack. Check joists or slab routes early. On most jobs, 40 mm pipe serves a shower well, with a 75 mm water-seal trap to stop smells.

• Follow local rules (UK: Building Regulations Part H for drainage, Part M for access). As a rule, aim for a 1:40 fall on 40 mm pipe. That’s about 25 mm drop over 1 metre.
• Keep the trap close to the outlet. Shorter runs drain better. Many contractors keep the trap within 300–600 mm of the pan outlet when space allows.
• Venting matters. If the run is long (over 3 m) or has several bends, plan a vent to stop gurgling and siphonage.

If you’re also looking to streamline professional proposals, our guide on professional proposals pairs well with this planning step.

Tools and Materials

• 40 mm solvent-weld or push-fit waste pipe and fittings
• 75 mm water-seal shower trap (low-profile if space is tight)
• 15 mm hot/cold supplies (copper or PEX), isolation valves
• Thermostatic mixer (set 38–41°C as a safe range)
• Sealant (sanitary silicone), PTFE tape, pipe clips
• Level, tape, holesaw (typically 52–55 mm for a 40 mm solvent socket), marker
• Test bungs, pressure gauge, and bucket for flood testing

Step-by-Step Low Pan Pipe Install

This is the practical sequence most plumbers follow on site.

1. Mark Out

   • Mark the tray footprint and outlet centre on the floor. Note the finished floor level.
   • Check trap height versus recess depth. A low-profile trap can save 10–20 mm.

2. Set the Fall

   • Plan the waste run at 1:40 (25 mm per metre). Use a level and packers to visualise the drop.
   • Avoid more than two 90° bends. Use 45° where possible to keep flow smooth.

3. Cut and Drill

   • Drill the outlet hole for the trap. A 52–55 mm holesaw suits many 40 mm solvent fittings.
   • If notching joists, follow structural rules. Keep services within safe zones and protect with plates.

4. Dry Fit Waste

   • Dry fit the trap to the pan. Then dry fit the 40 mm pipe to the stack branch.
   • Check the entire fall. Aim for a continuous drop, no bellies. Adjust clips every 400–600 mm to hold line.

5. Solvent or Push-Fit

   • For solvent-weld, clean and prime, then cement. Quarter turn and hold 10–15 seconds.
   • For push-fit, square cuts, deburr, lubricate seals, and fully home the pipe.

6. Venting and Bends

   • If the run is long or has three or more bends, plan a vent. AOSV (air admittance) can help if allowed by code.
   • Keep the vent leg rising vertically. Avoid flat spots where water can pool.

7. Connect Supplies

   • Run 15 mm hot and cold to the mixer. Fit isolation valves at an accessible point.

• Cap outlets. Pressurise to 1.5× working pressure for at least 10 minutes.
• Check every joint. Fix any weeps before boxing in.

11. Drain Test (Waste)

• Flood the tray to 20–30 mm depth for at least 15 minutes. No drops, no damp.
• Pull the plug. Watch the fall. Water should clear in under 30–60 seconds.

12. Seal and Cure

• Silicone the perimeter. Smooth and leave 24 hours to cure before use.
• Fit trims and test the shower at 10–12 litres per minute. Check for backup.

Waterproofing, Testing, and Handover

Waterproofing is the safety net. Use tanking on the floor and 300–500 mm up the wall, or as the tray maker states. Seal corners and penetrations. Then:

• Flood test: 20–30 mm standing water, 15 minutes minimum.
• Supply test: 10 minutes at 1.5× working pressure.
• Visual test: Run the shower for 2–3 minutes and inspect below (if accessible). Many contractors use a phone camera in tight voids to confirm dryness.

Record your tests. Photos of levels, trap, and fall lines help if there’s a callback.

Common Mistakes and Fast Fixes

• Trap Too High

  • Symptom: Pan won’t sit level. Fix: Use a low-profile trap or recess the floor an extra 10–15 mm if structure allows.

• Not Enough Fall

  • Symptom: Ponding, slow drain. Fix: Re-clip to regain 1:40. Swap a 90° bend for two 45°.

• Long Unvented Run

  • Symptom: Gurgling, odours. Fix: Add an air admittance valve (where permitted) or shorten the run.

• Over-Tightened Waste

  • Symptom: Deformed seal, small weeps. Fix: Re-seat washer and tighten hand-tight plus a quarter turn only.

• Skipping Flood Test

  • Symptom: Leaks show after tiling. Fix: Always flood test before sealing. This saves rework time.

If you’re pricing similar work, this pairs well with understanding invoice templates and managing project timelines so you capture every step and test in your client paperwork.

Pricing, Variations, and Documentation

Hidden snags are common: rotten joists, tight voids, and rerouting around steel. Protect your time.

• Define what’s included: tray type, trap profile, run length, venting, making good.
• List extras: concrete breaking, joist repairs, and moving stacks.
• Photos and notes: Before/after, fall checks, and test results.

To move fast from site notes to paperwork, many contractors use tools like Donizo to capture details on-site with Voice to Proposal, send branded PDFs for approval, and convert accepted proposals straight into invoices.

FAQ

What pipe size should I use for a low pan?

Most low pan pipe installs run on 40 mm waste with a 75 mm trap. It handles typical shower flows well (around 10–12 litres per minute) and keeps the seal deep enough to block smells.

What fall do I need on the waste?

Aim for 1:40 on 40 mm pipe. That’s a 25 mm drop per metre. Keep that fall continuous. Avoid bellies and sharp changes in direction. Two 45° bends flow better than a single 90° in tight spaces.

Do I need a vent for a short run?

Often no if the run is short (under about 3 m) with limited bends. If you hear gurgling or see slow drainage, add a vent or air admittance valve where allowed by local rules.

How long should I flood test a low pan?

Hold 20–30 mm of water in the tray for at least 15 minutes. Check underneath if you can. Any damp means you re-seat seals or rework joints before sealing and tiling.

Can I use push-fit for the waste?

Yes, if it’s rated for the application and fitted correctly. Many plumbers prefer solvent-weld for permanence under floors. For push-fit, make square cuts, deburr, and fully home the pipe.

Conclusion

A reliable low pan pipe install is simple when you plan the fall, keep the trap low, vent smartly, and test twice. Do these steps and your tray drains fast and stays dry.

Next steps:

• Measure and dry fit the waste at 1:40 today.
• Flood test to 20–30 mm for 15 minutes before sealing.
• Document tests and include them in your proposal.

For smoother paperwork, platforms such as Donizo help you turn on-site notes into clear proposals with e-signatures and one-click invoicing. Build a repeatable method, and every install gets easier.