When drainage has slowed

Water leaves fixtures more slowly than it used to.

What this page cannot establish

noticing this establishes that you noticed it — it does not establish a cause
this page cannot establish that the line is damaged
this page cannot establish that the line is not damaged
this page cannot establish how much of the line is involved

What a professional will be trying to work out

These are the distinctions a professional makes when they attend. They are questions, not conclusions — and knowing them lets you follow the conversation rather than just receive its result.

whether the change was gradual or sudden
how many fixtures show it
whether it varies with the amount of water used
whether it has ever fully blocked

What is worth writing down

These details are cheap to record now and impossible to reconstruct later.

approximately when it began
whether it was gradual or sudden
which fixtures are involved

Evidence that would change the next decision

If you are deciding whether something is worth paying for, these are the things that actually move the decision.

roughly when the change began
whether it affects fixtures on more than one level
whether it improves after a clearing and for how long

What would change the answer

roughly when the change began
whether it affects fixtures on more than one level
whether it improves after a clearing and for how long

What to do next

Whether a change was gradual or sudden is one of the first things a professional asks and one of the first things people forget.

Start a record before the detail fades

If your situation is different

It has blocked completely before: Blockages that keep coming back

Cleaning and maintenance
Cleaning is commonly the first thing discussed, and it is worth understanding what it establishes.