How to Set Up a 25mm Removable Grey-Water Waste System

September 2, 2026

25L grey-water tank connected to a removable 25mm campervan waste system

This guide covers Kiwi Self Contained's removable grey-water waste layout: a 25mm sink-waste connection, isolating ball valve, Camlock disconnect, separate 25L tank and separate 12mm exterior vent.

Products used

Separate 25L campervan water tank dedicated to grey water.
25mm removable-tank waste plumbing kit.
Separate 12mm waste-tank vent kit with a 2m or 3m hose option.
25mm 90-degree sink waste outlet with plug for a compatible sink.

Tools and consumables

Marker, tape measure and square.
Drill with a hole saw or step drill.
Deburring tool or fine file.
Spanners suitable for the fittings.
PTFE tape for compatible BSP threads.
Tank-compatible wastewater sealant where required by the fitting design.
Tank restraints, brackets or straps suitable for the vehicle.

The main 25mm tank connection commonly needs a hole of about 32mm. The 12mm vent connector commonly needs a hole of about 25mm. These are starting points only: measure the supplied fittings before drilling.

1. Plan the tank and hose positions

Choose a flat area low on the tank wall for the main waste connection, while leaving clearance inside for the 90-degree elbow. Position the vent connection high on the tank. Keep both holes clear of moulded feet, handles, corners and the screw cap.

2. Dry-fit the main outlet assembly

Before drilling, lay the fittings out in this order and confirm every thread position.

3. Drill and assemble the tank connection

Mark the hole centre and drill a small pilot hole.
Open the hole gradually with the measured hole saw or step drill.
Remove burrs without thinning or gouging the tank wall.
Clean and dry the sealing faces.
Apply PTFE tape only to compatible tapered threaded joints. Use suitable sealer for attaching plumbing parts to tank.
Assemble the elbow, nipple, washers and ball valve without twisting the tank wall. Tighten firmly, but do not over-tighten and deform the plastic.

4. Connect the sink waste hose

Fit the 25mm waste outlet to the compatible sink and leak-test the basin joint.
Push the female Camlock hose-tail fully into one end of the 25mm hose.
Connect the other end to the sink outlet.
Support the hose and form a water trap by looping the waste pipe.
Connect the Camlocks and close the dust cap over the exposed male fitting whenever the tank is disconnected.

5. Install the separate 12mm vent

Wastewater tanks need to vent directly to the exterior. Fit the tank vent connector high on the tank, then route the 12mm hose outside the vehicle. The outlet should be above the relevant flood level and away from doors, windows and other openings. Fit the mesh end filter or a suitable hooded cowl to prevent birds, insects and debris entering.

Keep the vent shut-off valve open while the system is in use. Close it only when disconnecting and moving the portable tank.

6. Secure and test the system

Secure the 25L tank so it cannot move or become a projectile while travelling.
Fill the fresh-water tank, run water through the sink and inspect every joint.
Check the sink drains freely and the vent does not leak water.
Close the ball valve before releasing the Camlock.
Fit the dust cap and close the vent shut-off before transporting the tank to an approved dump station.
After emptying, reconnect the tank and reopen the vent valve before using the sink.

Capacity and certification notes

Current inspection guidance recommends at least 12 litres of fresh-water storage per certified occupant and wastewater capacity not less than the fresh-water capacity. A 25L fresh tank and 25L grey-water tank can therefore provide the basic storage capacity for two occupants, provided the rest of the vehicle meets the requirements.

Official guidance recommends a minimum 20mm waste pipe from a sink and a minimum 12mm wastewater vent outlet. This Kiwi Self Contained system uses 25mm waste plumbing and a 12mm vent.