Blocked drain: what to try first

A blocked drain announces itself with water that goes down slowly, then not at all, and the first instinct is usually reasonable: try to shift it yourself before ringing anyone. Some of that is genuinely worth doing. Some of it makes the job worse for whoever opens the line next, us included.

A kitchen sink that drains slowly is often just grease and food matter sitting in the trap. Hot water is not going to fully clear a set grease plug, but a kettle of just-off-boil water poured slowly, twice, ten minutes apart, will sometimes shift a fresh blockage before it sets hard. For a bathroom drain running slow, a plunger over the waste, with the overflow blocked by hand or a wet cloth so it does not just push air sideways, is a fair first try.

If a single fixture is blocked and everything else in the house drains normally, the problem is almost always local to that fixture, which is good news: it is a smaller job and a smaller bill than a main line blockage.

Chemical drain cleaners are the main offender. They might shift a thin grease film, but they do nothing to tree roots or a genuinely broken pipe, and a caustic chemical sitting in a blocked line is not pleasant for whoever has to open that line with a machine or a camera next. If a drain has blocked twice in the same spot, stop pouring anything down it and call rather than reaching for a third bottle.

Coffee grounds, wet wipes marked "flushable", and cooking oil poured down a sink while still warm are the three most common causes we see on kitchen and laundry blockages, and none of them are obvious in the moment. Oil looks liquid going down and sets solid an hour later, well past the trap.

These look identical from above ground, which is exactly why the camera goes down the line before we call it finished. A grease blockage tends to build slowly over months, worse after big cooking days. Tree roots enter through a joint, not a crack, which is why root cutting alone rarely fixes it for good; the joint keeps letting more in behind whatever was cut. A broken or collapsed section blocks abruptly and often repeats within weeks no matter how thoroughly it is cleared, because clearing does not repair a structural fault.

Call straight away if more than one fixture is affected at once, if water is coming back up a different drain when you run one (a sign the blockage is downstream of both), or if there is any smell of sewage inside the house. Those point to a main line issue rather than a single fixture, and a main line blockage left running can back up into the lowest fixture in the house, which is a considerably bigger clean-up than the blockage itself.