BTO bedroom leaking at trunking: drain pipe sag from long run
A Sengkang BTO bedroom started leaking from the trunking even though the flat was not old. Newer estates can still have drainage issues when pipe runs are long. The question was whether the water was blocked, backflowing, or escaping from a sagging route.
By Team Snowflake | Reviewed 15 Jun 2026
Case summary
Daikin Wall-mounted4 years oldHDBSengkang, Singapore
- Concern
- Client expected another drain flush, but the leak kept returning after short-term clearing.
- Found
- Drain pipe sag causing water to collect inside a long trunking run
- Key check
- Checked drain fall through the trunking route before recommending cleaning alone
- Result
- The wet patch did not return after a full overnight run. The client had a route-level fix instead of another temporary drain clearing.
What we were told
The bedroom unit leaked near the trunking after running through the night. A previous drain clearing had helped briefly, but the same wet patch came back. The flat was relatively new, so the client did not expect a route issue. That made the repeated pattern more important than the age of the flat.
What we checked
Repeat leakage after a short-term flush made us check the drain route, not just the pipe opening. We ran water through the line and watched how it moved along the trunking. The issue was not that water could never pass; it was that water collected at a low section before slowly backing up.
Water could pass through the drain when pushed.
A low section inside the trunking held water after the test.
The first wet point matched the sagging section.
The indoor pan was not cracked and the coil was not icing.
What we found
The drain pipe had sagged along a long trunking run. Water travelled out of the indoor unit, then slowed and collected at the low point. During longer overnight use, that pocket filled enough for water to escape near the trunking. A basic flush could clear some dirt but could not correct the route. That is why the leak returned. The problem was the drain fall and support, not a failed indoor unit or a simple one-time choke. The newer building stock did not remove the need to check the actual drain path.
What fixed it
We corrected the drain support, restored fall through the affected section, and checked flow again before closing the trunking. We explained that future cleaning should not be the only response if the same wet point returns. The customer was shown where the route had sagged, because the flat being newer did not rule out installation or support issues. The practical fix was route correction plus normal cleaning, not repeated flushing.
Outcome
The wet patch did not return after a full overnight run. The client had a route-level fix instead of another temporary drain clearing.
What this case teaches us
Newer flats can leak from drain fall, not just drain choke
- A drain can be clear and still leak if the route sags. Water needs a steady fall all the way out.
- Long trunking runs in newer flats should be checked for support and low points, especially when leaks return after flushing.
- Ask whether the drain route was inspected, not only whether water was pushed through the pipe.
Related reading
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