What is happening
Warmth accelerates what is already sitting in the line, and dry weather empties traps that would otherwise hold a seal.
Drains report problems indirectly. The fixture showing the symptom is often not where the trouble is, which is why the useful first question is not what is blocked but which fixtures are affected and when.
What usually causes it
In this area, four explanations cover most cases:
- Waste sitting in a low section of the line
- A trap that dries out faster in warm weather
- Grease build-up decomposing in a kitchen branch
- A venting fault that is worse without air movement
Which one applies changes the fix entirely, and they are not distinguishable from inside the house. We would want to see it before saying anything for certain.
What you can check yourself
Run the fixtures one at a time and note which ones react to each other. Two drains that respond to one another share a pipe, and that narrows things considerably.
Note whether it is getting worse gradually or started suddenly. Gradual usually means the pipe has been closing up for a long time. Sudden usually means something specific is in the way.
Narrowing it down
Check whether the smell is at one fixture or general. One fixture points at that trap or branch. A general smell through the lower floor is more likely to be venting or something sitting in a shared line.
What guessing costs
Heat is not causing the problem, it is revealing it. Waiting for autumn makes the smell go away without changing anything about what is in the pipe.
When it is worth calling
If it has happened before, it is worth finding the cause rather than clearing it again. A drain that has been opened twice and returned twice will return a third time.
On this particular pattern, hydro jetting is the service that most often resolves it, though we would confirm that by looking rather than by assuming.
