diff --git a/nipype/interfaces/io.py b/nipype/interfaces/io.py
index 32e0fc76f1..ee26e94675 100644
--- a/nipype/interfaces/io.py
+++ b/nipype/interfaces/io.py
@@ -212,12 +212,12 @@ class DataSinkInputSpec(DynamicTraitedSpec, BaseInterfaceInputSpec):
     """
 
     # Init inputspec data attributes
-    base_directory = Directory(desc="Path to the base directory for storing data.")
+    base_directory = Str(desc="Path to the base directory for storing data.")
     container = Str(desc="Folder within base directory in which to store output")
     parameterization = traits.Bool(
         True, usedefault=True, desc="store output in parametrized structure"
     )
-    strip_dir = Directory(desc="path to strip out of filename")
+    strip_dir = Str(desc="path to strip out of filename")
     substitutions = InputMultiPath(
         traits.Tuple(Str, Str),
         desc=(
@@ -440,7 +440,6 @@ def _check_s3_base_dir(self):
             is not a valid S3 path, defaults to '<N/A>'
         """
 
-        # Init variables
         s3_str = "s3://"
         bucket_name = "<N/A>"
         base_directory = self.inputs.base_directory
@@ -449,22 +448,10 @@ def _check_s3_base_dir(self):
             s3_flag = False
             return s3_flag, bucket_name
 
-        # Explicitly lower-case the "s3"
-        if base_directory.lower().startswith(s3_str):
-            base_dir_sp = base_directory.split("/")
-            base_dir_sp[0] = base_dir_sp[0].lower()
-            base_directory = "/".join(base_dir_sp)
-
-        # Check if 's3://' in base dir
-        if base_directory.startswith(s3_str):
-            # Expects bucket name to be 's3://bucket_name/base_dir/..'
-            bucket_name = base_directory.split(s3_str)[1].split("/")[0]
-            s3_flag = True
-        # Otherwise it's just a normal datasink
-        else:
-            s3_flag = False
+        s3_flag = base_directory.lower().startswith(s3_str)
+        if s3_flag:
+            bucket_name = base_directory[len(s3_str):].partition('/')[0]
 
-        # Return s3_flag
         return s3_flag, bucket_name
 
     # Function to return AWS secure environment variables
@@ -618,13 +605,12 @@ def _upload_to_s3(self, bucket, src, dst):
 
         from botocore.exceptions import ClientError
 
-        # Init variables
         s3_str = "s3://"
         s3_prefix = s3_str + bucket.name
 
         # Explicitly lower-case the "s3"
-        if dst[: len(s3_str)].lower() == s3_str:
-            dst = s3_str + dst[len(s3_str) :]
+        if dst.lower().startswith(s3_str):
+            dst = s3_str + dst[len(s3_str):]
 
         # If src is a directory, collect files (this assumes dst is a dir too)
         if os.path.isdir(src):