Fats, oils and grease
Warm cooking fat is a liquid when it leaves the pan and a solid within a few metres of pipe, especially in an external run in a Scottish winter. Each layer traps the next, and over a few years the bore of a hundred millimetre pipe can narrow to the width of a finger. Once that has happened, anything that goes down will eventually bridge the gap.
Running the hot tap while you pour does not help. It moves the fat a little further along before it cools, which simply means the deposit forms in a less accessible part of the run. Pour fat into a tin or a jar, let it set and bin it.
Wet wipes, however they are marketed
Wipes are bonded fabric, not paper. They do not disintegrate in water within any meaningful timescale, and the word flushable on the packet describes only whether the item leaves the pan. In a perfect pipe they usually pass. In a pipe with a lipped joint, a slight dip or a few roots, they catch, and once one has caught the rest build on it.
Baby wipes, cleaning wipes, make up pads, cotton buds and dental floss all behave the same way. So does kitchen roll, which is designed to stay intact when wet and is a far more common cause of blocked toilets than people expect.
Sanitary items and nappies
These are designed to absorb liquid and expand, which is exactly the wrong property in a hundred millimetre pipe. A single nappy will block a soil pipe outright. Sanitary items and cotton wool swell and bind together with anything fibrous already in the run. Every bathroom needs a lidded bin, and in rented and commercial premises a clear sign next to it saves a great deal of money over a year.
Coffee grounds, rice, pasta and flour
Coffee grounds do not dissolve. They settle in the trap and in any part of the run holding water, and they bind with fat to form a dense sludge that a plunger will not move. Rice and pasta keep absorbing water and swelling after they have gone down. Flour and water is, quite literally, paste.
None of these are a problem in tiny quantities in a well fallen pipe with good flow. All of them are a problem in a kitchen run that already has a fat layer, which describes most kitchens over fifteen years old.
Chemicals, paint and building waste
- Caustic drain cleaners, which are a hazard to the next person to open the pipe and do nothing to structural faults.
- Paint and paint washings, which cure inside the pipe and are extremely difficult to remove.
- Plaster, tile adhesive and grout washings, which set hard in the trap and often mean the section has to be cut out.
- Cat litter, which is designed to clump and is one of the worst things to put into any drain.
- Engine oil and white spirit, which are pollutants and should go to a recycling centre.
Habits that prevent call outs
A fat trap or grease container by the hob, a strainer in every plughole, a lidded bin in every bathroom and a two minute clear out of the external gully each season will prevent the majority of the blockages we attend. In a commercial kitchen add a properly sized grease trap and a written cleaning schedule, because environmental health will ask about both.
Where a property has already had repeat blockages, the pipe usually has a deposit or a defect and preventive habits alone will not be enough. A jet and a camera once will tell you which, and after that maintenance can be targeted rather than hopeful.
What to do if something has already gone down
If an object has been dropped down a toilet or a gully, do not flush repeatedly hoping it will pass. Each flush pushes it further into the run and turns a retrievable item into an excavation. Stop using the appliance and tell the engineer exactly what went down and roughly when.
Where fat or building waste has been going down for years, the deposit is already on the pipe wall and no change of habit will remove it. A single jetting visit strips it back, and a camera check afterwards confirms the bore is genuinely clear. From that point good habits keep it that way, which is a much cheaper position to be in.
Questions we get asked
Are flushable wipes ever safe?
Only in the sense that they leave the toilet pan. They do not break down in the drain and are a leading cause of the blockages we clear.
Is a food waste disposal unit a good idea?
It reduces solids in the bin but increases fine organic matter in the pipe, so it needs a well fallen run and regular flushing to be trouble free.
Can I pour bleach down the drain?
Normal household use is fine. It is concentrated caustic drain products, not bleach, that create the hazard for engineers.
What about milk or beer down the sink?
Small quantities are fine at home. In licensed premises, regular volumes of waste beer and milk feed bacterial growth and smell, and need a maintained trap.