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. Subsoil and stormwater drainage must comply with AS/NZS 3500.3 (the national plumbing and drainage standard that specifies pipe falls, trench bedding depths, and approved discharge points to stop groundwater from pooling against building foundations). Pipe fall, bedding, drainage aggregate, geotextile filter fabric 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. In NSW, drainage connections are regulated plumbing work carried out under Building Commission NSW Contractor Licence 305428C and Qualified Supervisor oversight.
Sydney property owners have trusted and turned to Fixed Today across decades for clear, practical subsoil and drainage solutions. When you reach out, our team asks a few targeted pre-dispatch questions about your property's ground conditions—such as surface pooling symptoms, soil type, and whether your footings sit on sandstone or reactive clay—so our truck arrives stocked with the right trenching, levelling, and drainage gear. Contact our Sydney stormwater drainage team for supportive on-site guidance, where we break down each step of the drainage installation with fixed upfront pricing and a $0 call-out on approved work.