diff --git a/src/pathsim_chem/tritium/bubbler.py b/src/pathsim_chem/tritium/bubbler.py
index 9485ae4..1d5beea 100644
--- a/src/pathsim_chem/tritium/bubbler.py
+++ b/src/pathsim_chem/tritium/bubbler.py
@@ -93,6 +93,18 @@ class Bubbler4(DynamicalSystem):
     of a full vial with an empty one.
     """
 
+    input_port_labels = {
+        "sample_in_soluble": 0,
+        "sample_in_insoluble": 1,
+        }
+    output_port_labels = {
+        "vial1": 0,
+        "vial2": 1,
+        "vial3": 2,
+        "vial4": 3,
+        "sample_out": 4,
+        }
+
     def __init__(
         self,
         conversion_efficiency=0.9,
@@ -144,25 +156,6 @@ def _fn_a(x, u, t):
             initial_value=np.zeros(4),
             )
 
-        # define port maps 
-        self.inputs = Register(
-            size=2, 
-            mapping={
-                "sample_in_soluble": 0,
-                "sample_in_insoluble": 1,
-                },
-            )
-        self.outputs = Register(
-            size=5, 
-            mapping={
-                "vial1": 0,
-                "vial2": 1,
-                "vial3": 2,
-                "vial4": 3,
-                "sample_out": 4,
-                },
-            )
-
         #create internal vial reset events
         self._create_reset_events()
 
diff --git a/src/pathsim_chem/tritium/glc.py b/src/pathsim_chem/tritium/glc.py
index 56bb47a..63dffa6 100644
--- a/src/pathsim_chem/tritium/glc.py
+++ b/src/pathsim_chem/tritium/glc.py
@@ -364,6 +364,23 @@ class GLC(pathsim.blocks.Function):
         BCs: Boundary conditions type, "C-C" (Closed-Closed) or "O-C" (Open-Closed), default is "C-C"
     """
 
+    input_port_labels = {
+        "c_T_in": 0,
+        "flow_l": 1,
+        "y_T2_inlet": 2,
+        "flow_g": 3,
+        }
+    output_port_labels = {
+        "c_T_out": 0,
+        "y_T2_out": 1,
+        "eff": 2,
+        "P_out": 3,
+        "Q_l": 4,
+        "Q_g_out": 5,
+        "n_T_out_liquid": 6,
+        "n_T_out_gas": 7,
+        }
+
     def __init__(
         self,
         P_in,
@@ -385,29 +402,6 @@ def __init__(
         }
         super().__init__(func=self.func)
 
-        self.inputs = Register(
-            size=4,
-            mapping={
-                "c_T_in": 0,
-                "flow_l": 1,
-                "y_T2_inlet": 2,
-                "flow_g": 3,
-            },
-        )
-        self.outputs = Register(
-            size=8,
-            mapping={
-                "c_T_out": 0,
-                "y_T2_out": 1,
-                "eff": 2,
-                "P_out": 3,
-                "Q_l": 4,
-                "Q_g_out": 5,
-                "n_T_out_liquid": 6,
-                "n_T_out_gas": 7,
-            },
-        )
-
     def func(self, c_T_in, flow_l, y_T2_inlet, flow_g):
         new_params = self.params.copy()
         new_params["c_T_in"] = c_T_in
diff --git a/src/pathsim_chem/tritium/residencetime.py b/src/pathsim_chem/tritium/residencetime.py
index c06e797..157253f 100644
--- a/src/pathsim_chem/tritium/residencetime.py
+++ b/src/pathsim_chem/tritium/residencetime.py
@@ -115,13 +115,9 @@ class Process(ResidenceTime):
         initial value of state / initial quantity of process
     source_term : float
         constant source term / generation term of the process
-    """
+    """    
+    input_port_labels = None
+    output_port_labels = {"x": 0, "x/tau": 1}
 
     def __init__(self, tau=1, initial_value=0, source_term=0):
-        super().__init__(tau, 1, [1, 1/tau], initial_value, source_term)
-
-        # define output port maps based on fractions
-        self.outputs = Register(
-            size=2, 
-            mapping={"x": 0, "x/tau": 1}
-            )
\ No newline at end of file
+        super().__init__(tau, 1, [1, 1/tau], initial_value, source_term)
\ No newline at end of file
diff --git a/src/pathsim_chem/tritium/splitter.py b/src/pathsim_chem/tritium/splitter.py
index ee4ebbd..b987a31 100644
--- a/src/pathsim_chem/tritium/splitter.py
+++ b/src/pathsim_chem/tritium/splitter.py
@@ -29,6 +29,9 @@ class Splitter(Function):
         must sum up to one
     """
 
+    input_port_labels = {"in": 0}
+    output_port_labels = None
+
     def __init__(self, fractions=None):
 
         self.fractions = np.ones(1) if fractions is None else np.array(fractions)
@@ -38,14 +41,4 @@ def __init__(self, fractions=None):
             raise ValueError(f"'fractions' must sum to one and not {sum(self.fractions)}")
 
         # initialize like `Function` block
-        super().__init__(func=lambda u: self.fractions*u)
-
-        # define port maps based on fractions
-        self.inputs = Register(
-            size=1, 
-            mapping={"in": 0}
-            )
-        self.outputs = Register(
-            size=len(self.fractions), 
-            mapping={f"out {fr}": i for i, fr in enumerate(self.fractions)}
-            )
\ No newline at end of file
+        super().__init__(func=lambda u: self.fractions*u)
\ No newline at end of file