For a partially perforated subsoil or agricultural drain, the holes generally face down, in the lower part of the pipe. Follow the manufacturer’s markings and instructions if they specify a different perforated drain pipe orientation. This does not apply to solid waste pipes from fixtures.
Why the holes face down
Downward-facing openings allow groundwater moving through the drainage aggregate to enter near the bottom of the trench. If the holes face up, water generally needs to rise higher around the pipe before entering.
Orientation is only one part of an effective installation. Pipe fall, bedding, drainage aggregate, filter material and the discharge point must suit the product and site.
Check the perforation pattern
- Partially perforated pipe: Place the holes or slots in the lower portion, following the product markings or instructions.
- Fully slotted pipe: If slots run around the full circumference, rotation generally makes no practical difference. Check for any manufacturer-specified orientation.
- Outlet and connections: Use a lawful discharge point suitable for the site. Connection requirements vary, so do not assume a subsoil drain can connect to a sewer, stormwater system or surface outlet.
Keep the pipe aligned during joining and backfilling, as lightweight pipe can rotate.
After installation, regulated drainage may need testing before it is covered or put into service.
Before excavating, check Before You Dig Australia plans and have underground services located. Stop if their positions are uncertain. Excavation and drainage connections can involve concealed services and regulated work; use an appropriately licensed plumber or drainer where required in NSW.
If the pipe markings, orientation or permitted outlet are unclear, contact our Sydney plumbing team for site-specific advice.