Dry cleansing with stone or an equivalent suffices at the normal exit if the area is actually cleansed.
Washing with water is superior as it can remove traces that dry rubbing may leave behind.
If impurity spreads beyond the exit, the general dry-cleansing permission becomes restricted.
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Istinja: Methods, Preference and Juristic Differences
Dry cleansing with stone or an equivalent suffices at the normal exit if the area is actually cleansed.
Washing with water is superior as it can remove traces that dry rubbing may leave behind.
If impurity spreads beyond the exit, the general dry-cleansing permission becomes restricted.