diff --git a/zfs-backup.py b/zfs-backup.py
index e0d2252..dc1a686 100755
--- a/zfs-backup.py
+++ b/zfs-backup.py
@@ -96,16 +96,13 @@ class Manager:
 
     @staticmethod
     def _find_snapshots_with_backup_tag(dataset: Dataset) -> list[Snapshot]:
-        regex = Manager._get_regex_matching_backup_tags()
+        regex = _get_regex_matching_snapshots_with_tags(
+            [config.snapshot_tag, config.snapshot_interval]
+        )
         return [
             snapshot for snapshot in dataset.snapshots if snapshot.matches_regex(regex)
         ]
 
-    @staticmethod
-    # TODO make function
-    def _get_regex_matching_backup_tags():
-        return "@" + ".*".join([config.snapshot_tag, config.snapshot_interval])
-
     @staticmethod
     def _search_matching_dataset_in_remote_pool(dataset: Dataset, pool: Pool):
         dataset_to_search = dataset.replace_pool(pool.name)
@@ -125,6 +122,10 @@ class Manager:
         return common_snapshots[-1]
 
 
+def _get_regex_matching_snapshots_with_tags(tags: list[str]):
+    return "@" + ".*".join(tags)
+
+
 class ZFSPath:
     def __init__(self, elements: list[str], snapname: Optional[str] = None):
         self._elements = elements
@@ -433,16 +434,19 @@ class Dataset:
             self._clean_old_snapshots_for_interval(interval, number)
 
     def _clean_old_snapshots_for_interval(self, interval: str, max_count: int):
-        # TODO this is somewhat similar to the regex method in Manager
-        regex = ".*".join(["", config.snapshot_tag, interval, ""])
+        regex = _get_regex_matching_snapshots_with_tags(
+            [config.snapshot_tag, interval]
+        )
         snapshots = [
             snapshot for snapshot in self.snapshots if snapshot.matches_regex(regex)
         ]
-        # TODO function _get_n_oldest_snapshots
-        if len(snapshots) > max_count:
-            snapshots.sort()
-            for snap in snapshots[:-max_count]:
-                snap.destroy()
+        old_snapshots = self._get_n_oldest_snapshots(snapshots, max_count)
+        for snapshot in old_snapshots:
+            snapshot.destroy()
+
+    def _get_n_oldest_snapshots(self, snapshots: list[Snapshot], count: int) -> list[Snapshot]:
+        snapshots.sort()
+        return snapshots[:count]
 
 
 class Snapshot: