Drain plugs are a small but critical component of any campervan water system. A failing drain plug leaks grey water into your van cupboard, lets fresh water drain out during winter storage, or cracks when you overtighten it. The right plug lasts years. The wrong one fails at the worst moment.
This guide covers the types of drain plugs used in UK campervan builds, what fits which system, and where to buy replacements.
Where Drain Plugs Are Used
A typical campervan water system has three or four drain points:
- Kitchen sink — the plug that seals the sink bowl for washing up. Usually a standard 40mm or 45mm basket strainer plug.
- Sink drain tail — where the sink waste pipe connects to the grey water tank. Some builds use a removable plug here for winterising.
- Grey water tank outlet — a drain plug at the lowest point of the grey water tank for emptying and cleaning. Usually 1/2" BSP or 3/4" BSP threaded fitting.
- Fresh water tank drain — a plug at the bottom of the fresh water tank for draining before winter or long storage.
- Water heater drain — if you have a calorifier or instant water heater, there is usually a drain plug for winterising.
Types of Drain Plugs
Basket Strainer Plugs (Sink)
The standard UK kitchen sink plug. Two common types:
- Push-fit pop-up plug — a spring-loaded mechanism integrated into the basket strainer. Push to close, push again to open. Convenient but prone to sticking in hard water areas. Replacing the rubber seal costs about £2. The whole mechanism costs £8–£15.
- Standard rubber plug — a simple rubber stopper on a chain. Unbreakable, cheap (£2–£4), and universally available. The rubber perishes after 12–18 months in a van due to temperature swings.
For van use, the simple rubber plug is more reliable. The pop-up mechanism's spring corrodes in the damp environment under a van sink.
Threaded Drain Plugs (Tanks)
Tank drain plugs use British Standard Pipe (BSP) threads, which are the standard for UK plumbing.
1/2" BSP plug — the most common size for campervan fresh water and grey water tank drains. External thread diameter: approximately 21mm. Pitch: 14 threads per inch.
3/4" BSP plug — used on larger tank outlets and some water heater drains. External thread diameter: approximately 26mm.
15mm compression cap — sometimes used on the outlet of flexible hoses where a formal tank outlet is not fitted. Not a drain plug in the traditional sense but serves the same function.
The thread type matters. BSP threads are parallel (straight), not tapered like NPT (National Pipe Thread) fittings common in US vans. A US-sourced plug will not seal in a UK van's tank fitting and vice versa.
Push-Fit Drain Plugs
Some UK van conversions use push-fit plumbing (John Guest Speedfit, Hep2O) for water lines. These use a collet-and-O-ring system where the pipe pushes in and a locking ring holds it.
Push-fit systems do not have traditional drain plugs. To drain the system, you either pull the pipe at its lowest connection point or install a dedicated drain valve (John Guest do an isolation valve with a drain function for about £8). If your van uses push-fit plumbing, do not try to install a standard BSP plug — the thread will not match.
Lever-Operated Drain Valves
A lever valve installed on the tank outlet is more convenient than a threaded plug — no tools needed, no dropped plugs in the mud at the service point. The standard is a 1/2" BSP lever valve with a hose tail. Turn the lever 90 degrees to open/close.
Cost: £5–£12 from any UK plumbing merchant (Screwfix, Toolstation, Plumbase). Specify "full bore" for better flow when draining grey water, which contains solids.
Materials
| Material | Use Case | Pros | Cons |
|---|---|---|---|
| Brass | Threaded tank plugs | Durable, good thread engagement, corrosion-resistant | Heavy, more expensive (£6–£12) |
| Stainless steel | Threaded tank plugs | Very durable, lightweight, no corrosion | Expensive (£8–£15), can gall (seize) on brass threads |
| Nylon / acetal | Tank plugs, push-fit fittings | Lightweight, cheap (£2–£5), rot-proof | Can crack if overtightened, UV degrades over time |
| Rubber | Sink plugs | Cheap (£2–£4), effective seal, universal | Perishes in UV and heat, wears out annually |
| Chrome-plated brass | Sink basket strainers | Looks good, easy to clean | Chrome peels in hard water, brass core still fine |
For tank drain plugs in a van, use nylon/acetal or brass. Stainless steel looks better but has a higher tendency to seize in threaded fittings due to galling — when stainless steel threads tighten against each other, they can cold-weld and become impossible to remove.
Winterising and Drain Plugs
Before winter storage, every water system component must be drained to prevent freeze damage. Drain plugs are the access points for this.
The process:
- Open all drain plugs and taps
- Open the sink basket strainer to allow air into the system
- Disconnect the lowest point in the water line (usually where the pipe exits the fresh water tank) and let gravity drain the system
- Blow through the system if possible — a lungful of air through the filler cap forces residual water out of low points
- Leave all drain plugs and taps open over winter. Do not tighten them
In the spring, close all drain plugs, fill the system, and check each plug for leaks. Nylon plugs sometimes shrink in cold weather and need re-tightening after the first fill.
Where to Buy Drain Plugs in the UK
| Supplier | Range | Notes |
|---|---|---|
| Screwfix | Brass and nylon BSP plugs, lever valves, push-fit fittings | Convenient, many branches, good price |
| Toolstation | Same range as Screwfix, slightly lower prices | Same-day delivery in some areas |
| BES Ltd | Specialist brassware, every BSP size | Best for odd sizes |
| Amazon UK | Everything, but check seller | Counterfeit brass fittings exist — buy from branded sellers |
| Van conversion specialists | Pre-selected kits with correct fittings | Convenient but marked up 30–50% |
| Caravan breaker yards | Used fittings from salvaged vans | Cheap, but check threads carefully |
For a full van water system, budget £15–£25 for all drain plugs and fittings.
Common Problems
Leaking Threaded Plug
The plug tightens but water still leaks past the threads. Solution: use PTFE tape (plumber's tape) on the plug threads. Wrap three layers clockwise (when looking at the plug face). If it still leaks, the thread is damaged — replace the plug. Do not use silicone sealant on tank plugs; it makes the next removal difficult and contaminates the water.
Plug Will Not Fit
The thread is slightly different. You may have a BSP plug and a BSPT (tapered) fitting, or vice versa. BSPP (parallel) and BSPT (tapered) are not compatible. Check which your tank uses by measuring the thread with a thread gauge. If unsure, take the old plug to a plumbing merchant and ask them to match it.
Plug Corroded in Place (Brass)
Brass plugs in brass fittings can corrode together after years in contact with water. Use a penetrating oil (WD-40, PlusGas) and leave it for 30 minutes before attempting to unscrew. Use a proper spanner (not adjustable pliers) to avoid rounding the hex head. If the hex is already rounded, use a socket set.
Plug Cracked (Nylon)
Nylon plugs crack when overtightened. Hand-tight plus a quarter turn with a spanner is sufficient. If the crack is hairline and the plug is not leaking, leave it until the next drain-down then replace.
Related Reading
- Cassette Toilet Emptying UK
- Underslung vs Internal Water Tanks
- Winterising Your Van's Water System
- Flojet vs Shurflo Pumps Comparison
