Start with the symptoms
One slow fixture or a recurring backup?
The location and pattern are useful information. Note whether the issue is limited to a sink, tub or shower, or whether several drains are behaving differently. Odors and recurring backups also belong in the conversation, including whether they occur after particular fixtures are used.
Grease, foreign material or root intrusion can be involved in a blockage, but those are possible findings rather than a diagnosis based on the symptom alone. An assessment helps establish what is restricting the line and whether cleaning is a reasonable next step. Tell us about earlier drain work so we can consider the history.
