diff --git a/.gitignore b/.gitignore
index 3fcc0393..1f66efca 100644
--- a/.gitignore
+++ b/.gitignore
@@ -17,8 +17,6 @@ _build
 prof
 *Pyreverse*
 monkeytype.sqlite3
-
-# Spyder
 *.spyproject*
 
 # Docs #
diff --git a/docs/source/tutorials/3_WasteStream.ipynb b/docs/source/tutorials/3_WasteStream.ipynb
index c1228f01..11ff9a96 100644
--- a/docs/source/tutorials/3_WasteStream.ipynb
+++ b/docs/source/tutorials/3_WasteStream.ipynb
@@ -28,7 +28,7 @@
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "This tutorial is made with qsdsan v0.3.2.\n"
+      "This tutorial is made with qsdsan v0.3.5.\n"
      ]
     }
    ],
@@ -260,7 +260,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 2,
+   "execution_count": 10,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -270,7 +270,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 10,
+   "execution_count": 11,
    "metadata": {},
    "outputs": [
     {
@@ -368,7 +368,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 11,
+   "execution_count": 12,
    "metadata": {},
    "outputs": [
     {
@@ -409,7 +409,7 @@
        "                <H2O: 981.47 kg/hr>])"
       ]
      },
-     "execution_count": 11,
+     "execution_count": 12,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -424,7 +424,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 12,
+   "execution_count": 13,
    "metadata": {},
    "outputs": [
     {
@@ -451,7 +451,7 @@
        "       1.200e-02, 5.448e+01])"
       ]
      },
-     "execution_count": 12,
+     "execution_count": 13,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -465,7 +465,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 13,
+   "execution_count": 14,
    "metadata": {},
    "outputs": [
     {
@@ -508,7 +508,7 @@
        "                <H2O: 0.9844 m^3/hr>])"
       ]
      },
-     "execution_count": 13,
+     "execution_count": 14,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -521,7 +521,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 14,
+   "execution_count": 15,
    "metadata": {},
    "outputs": [
     {
@@ -539,7 +539,7 @@
        "       1.200e+01, 9.815e+05])"
       ]
      },
-     "execution_count": 14,
+     "execution_count": 15,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -551,7 +551,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 15,
+   "execution_count": 16,
    "metadata": {},
    "outputs": [
     {
@@ -572,7 +572,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 16,
+   "execution_count": 17,
    "metadata": {},
    "outputs": [
     {
@@ -634,7 +634,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 17,
+   "execution_count": 18,
    "metadata": {},
    "outputs": [
     {
@@ -666,7 +666,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 18,
+   "execution_count": 19,
    "metadata": {},
    "outputs": [
     {
@@ -731,7 +731,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 19,
+   "execution_count": 20,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -742,7 +742,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 20,
+   "execution_count": 21,
    "metadata": {},
    "outputs": [
     {
@@ -759,7 +759,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 21,
+   "execution_count": 22,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -772,7 +772,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 22,
+   "execution_count": 23,
    "metadata": {},
    "outputs": [
     {
@@ -798,7 +798,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 23,
+   "execution_count": 24,
    "metadata": {},
    "outputs": [
     {
@@ -831,7 +831,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 24,
+   "execution_count": 25,
    "metadata": {},
    "outputs": [
     {
@@ -840,7 +840,7 @@
        "251.9652894584042"
       ]
      },
-     "execution_count": 24,
+     "execution_count": 25,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -853,7 +853,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 25,
+   "execution_count": 26,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -866,7 +866,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 26,
+   "execution_count": 27,
    "metadata": {},
    "outputs": [
     {
@@ -889,7 +889,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 27,
+   "execution_count": 28,
    "metadata": {},
    "outputs": [
     {
@@ -916,7 +916,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 28,
+   "execution_count": 29,
    "metadata": {},
    "outputs": [],
    "source": [
@@ -925,7 +925,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 29,
+   "execution_count": 30,
    "metadata": {},
    "outputs": [
     {
@@ -934,7 +934,7 @@
        "77.01571037585582"
       ]
      },
-     "execution_count": 29,
+     "execution_count": 30,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -947,7 +947,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 30,
+   "execution_count": 31,
    "metadata": {},
    "outputs": [
     {
@@ -956,7 +956,7 @@
        "0.0"
       ]
      },
-     "execution_count": 30,
+     "execution_count": 31,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -968,7 +968,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 31,
+   "execution_count": 32,
    "metadata": {},
    "outputs": [
     {
@@ -977,7 +977,7 @@
        "0.0"
       ]
      },
-     "execution_count": 31,
+     "execution_count": 32,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -989,7 +989,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 32,
+   "execution_count": 33,
    "metadata": {},
    "outputs": [
     {
@@ -998,7 +998,7 @@
        "80.62889262668934"
       ]
      },
-     "execution_count": 32,
+     "execution_count": 33,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -1010,7 +1010,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 33,
+   "execution_count": 34,
    "metadata": {},
    "outputs": [
     {
@@ -1019,7 +1019,7 @@
        "485.2265687216927"
       ]
      },
-     "execution_count": 33,
+     "execution_count": 34,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -1031,7 +1031,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 34,
+   "execution_count": 35,
    "metadata": {},
    "outputs": [
     {
@@ -1040,7 +1040,7 @@
        "13.99807163657801"
       ]
      },
-     "execution_count": 34,
+     "execution_count": 35,
      "metadata": {},
      "output_type": "execute_result"
     }
@@ -1074,7 +1074,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython3",
-   "version": "3.8.2"
+   "version": "3.8.11"
   }
  },
  "nbformat": 4,
diff --git a/qsdsan/_sanunit.py b/qsdsan/_sanunit.py
index 2b63aad3..b8e1d684 100644
--- a/qsdsan/_sanunit.py
+++ b/qsdsan/_sanunit.py
@@ -372,8 +372,17 @@ def results(self, with_units=True, include_utilities=True,
             results.loc[('Additional OPEX', ''), :] = ('USD/hr', 0)
         else:
             for k, v in self.add_OPEX.items():
-                try: results.loc[(k, ''), :] = ('USD/hr', v)
-                except: breakpoint()
+                if not with_units:
+                    results.loc[(k, '')] = v
+                else:
+                    try: results.loc[(k, ''), :] = ('USD/hr', v)
+                    # When `results` is a series instead of dataframe,
+                    # might not need this
+                    except ValueError:
+                        results = results.to_frame(name=self.ID)
+                        results.insert(0, 'Units', '')
+                        results.loc[(k, ''), :] = ('USD/hr', v)
+                        results.columns.name = type(self).__name__
         if with_units:
             results.replace({'USD': f'{currency}', 'USD/hr': f'{currency}/hr'},
                             inplace=True)
diff --git a/qsdsan/_waste_stream.py b/qsdsan/_waste_stream.py
index a72d9651..ea979d16 100644
--- a/qsdsan/_waste_stream.py
+++ b/qsdsan/_waste_stream.py
@@ -26,7 +26,8 @@
 # %%
 
 import numpy as np
-from thermosteam import settings
+from free_properties import PropertyFactory, property_array
+from thermosteam import settings, indexer
 from . import Components, Stream, MultiStream, SanStream, MissingSanStream, \
     set_thermo
 from .utils import auom, copy_attr
@@ -119,6 +120,69 @@ def _calib_XBsub_fBODCOD(components, concentrations, substrate_IDs, BOD):
     return fbodtocod_sub
 
 
+# Indexer for nicer display
+@property
+def group_conc_compositions(self):
+    raise AttributeError('cannot set group by concentratino')
+
+ComponentConcentrationIndexer, ConcentrationIndexer = \
+    indexer._new_Indexer('Concentration', 'mg/L', group_conc_compositions)
+
+ChemicalMolarFlowIndexer = indexer.ChemicalMolarFlowIndexer
+
+@PropertyFactory(slots=('name', 'mol', 'index', 'F_vol', 'MW',
+                        'phase', 'phase_container'))
+def ConcentrationProperty(self):
+    '''Concentration flow, in mg/L (g/m3).'''
+    f_mass = self.mol[self.index] * self.MW
+    phase = self.phase or self.phase_container.phase
+    if phase != 'l':
+        raise AttributeError('Concentration only valid for liquid phase.')
+    V_sum = self.F_vol
+    if V_sum==0:
+        raise RuntimeError('WasteStream is empty, concentration cannot be calculated.')
+    return 1000. * f_mass / V_sum if f_mass else 0.
+@ConcentrationProperty.setter
+def ConcentrationProperty(self, value):
+    raise AttributeError('Cannot set flow rate by concentration.')
+
+def by_conc(self, TP):
+    '''
+    Return a ComponentConcentrationIndexer that references this object's
+    molar and volume data (volume relies on molar).
+
+    Parameters
+    ----------
+    TP : ThermalCondition
+
+    '''
+    try:
+        conc = self._data_cache[TP]
+    except:
+        cmps = self.chemicals
+        mol = self.data
+        F_vol = self.by_volume(TP).data.sum()
+        conc = np.zeros_like(mol, dtype=object)
+        for i, cmp in enumerate(cmps):
+            conc[i] = ConcentrationProperty(cmp.ID, mol, i, F_vol, cmp.MW,
+                                            None, self._phase)
+        self._data_cache[TP] = \
+        conc = ComponentConcentrationIndexer.from_data(property_array(conc),
+                                                      self._phase, cmps,
+                                                      False)
+    return conc
+indexer.ChemicalMolarFlowIndexer.by_conc = by_conc
+
+def by_conc(self, TP):
+    '''
+    Raise an error for attempt multi-phase usage
+    as concentration only valid for liquid).
+    '''
+    raise AttributeError('Concentration only valid for liquid phase.')
+
+indexer.MolarFlowIndexer.by_conc = by_conc; del by_conc
+del PropertyFactory
+
 
 # %%
 
@@ -627,10 +691,24 @@ def dry_mass(self):
     # def charge(self):
     #     return self._liq_sol_properties('charge', self.composite('charge'))
 
+
+
+    @property
+    def iconc(self):
+        '''[Indexer] Mass concentrations, in mg/L (g/m3).'''
+        return self._imol.by_conc(self._thermal_condition)
+
     @property
-    def Conc(self):
-        '''Mass concentrations, in g/m3.'''
-        return self.get_mass_concentration()
+    def conc(self):
+        '''[property_array] Mass concentrations, in mg/L (g/m3).'''
+        return self.iconc.data
+        # mass = self.mass
+        # try: mass[:] = self.get_mass_concentration()
+        # except: breakpoint()
+        # printed = mass.__repr__()
+        # printed = printed.replace('kg/hr', 'mg/L')
+        # print(printed)
+        # return printed
 
 
     def copy(self, new_ID='', ws_properties=True):
diff --git a/qsdsan/sanunits/_uddt.py b/qsdsan/sanunits/_uddt.py
index f6d7a308..24ae7d51 100644
--- a/qsdsan/sanunits/_uddt.py
+++ b/qsdsan/sanunits/_uddt.py
@@ -70,7 +70,7 @@ class UDDT(Toilet):
 
     def __init__(self, ID='', ins=None, outs=(), thermo=None, init_with='WasteStream',
                  degraded_components=('OtherSS',), N_user=1, N_toilet=1, lifetime=8,
-                 if_toilet_paper=True, if_flushing=True, if_cleansing=False,
+                 if_toilet_paper=True, if_flushing=False, if_cleansing=False,
                  if_desiccant=True, if_air_emission=True, if_ideal_emptying=True,
                  CAPEX=553, OPEX_over_CAPEX=0.1,
                  T=273.15+24, safety_factor=1, if_prep_loss=True, if_treatment=False,
diff --git a/qsdsan/utils/getters.py b/qsdsan/utils/getters.py
index f58da036..e6301f13 100644
--- a/qsdsan/utils/getters.py
+++ b/qsdsan/utils/getters.py
@@ -20,14 +20,15 @@
 
 
 class AttrGetter:
-    __slots__ = ('obj', 'attr', 'hook')
-    def __init__(self, obj, attr, hook=lambda i: i):
+    __slots__ = ('obj', 'attr', 'hook', 'hook_param')
+    def __init__(self, obj, attr, hook=lambda i: i, hook_param=None):
         self.obj = obj
         self.attr = attr
         self.hook = hook
+        self.hook_param = hook_param
 
     def __call__(self):
-        return self.hook(getattr(self.obj, self.attr))
+        return self.hook(getattr(self.obj, self.attr), *self.hook_param)
 
 # # The below one needs updating
 # class AttrGetter: