- Material
- Fats, oils and grease (FOG)
- Common starting point
- Kitchen discharge
- Possible extent
- Trap, waste pipe or downstream drain
- Useful clue
- Whether other fixtures also drain slowly
How fat, oil and grease build up in drains
Fats and oils discharged into kitchen drainage can form deposits and collect other material. Water UK describes how fats, oils, grease and unflushable items combine in sewer blockages. A restriction first noticed at a sink may therefore extend beyond the visible waste pipe.
Food residue should be kept out of the drain and cooking fats should not be poured into the sink. Foodservice businesses should use suitable equipment to keep fats, oils, grease and food solids out of drains, and maintain that equipment properly.
Local waste-pipe or downstream restriction
A single sink draining slowly can indicate a problem in the trap or local waste pipe. If several fixtures are affected, or water backs up at an outside drain, the restriction may be further downstream. Odour on its own does not establish that grease is the cause.
A sink that becomes noticeably slower during heavy use may simply be making an existing restriction more obvious. That pattern is useful, but inspection is still needed before the cause is confirmed.
Removing grease deposits
The clearance method depends on access, pipe condition and where the deposit has formed. The work also needs to avoid creating a new restriction further downstream, particularly where grease-management equipment is fitted.
Repeated flushing with hot water or adding chemicals is not a repair for a substantial grease blockage. Cleaning products should not be mixed. If the system is overflowing, adding more water can increase the escape of wastewater.
Recurring grease blockages
If grease returns after clearance, it is worth checking whether fats are still entering the system and whether grease-management equipment is being maintained. Repeated deposits can also justify investigation of the pipework for defects or places where solids are catching.