Index: firmware/App/Controllers/DGInterface.c
===================================================================
diff -u -r1a685471524555a374854c0c9ec8e208e71fe2df -r85ab84d9a0668e1e3976b00eb29e79c38c81b651
--- firmware/App/Controllers/DGInterface.c	(.../DGInterface.c)	(revision 1a685471524555a374854c0c9ec8e208e71fe2df)
+++ firmware/App/Controllers/DGInterface.c	(.../DGInterface.c)	(revision 85ab84d9a0668e1e3976b00eb29e79c38c81b651)
@@ -83,7 +83,8 @@
 static U32 dgReservoirDrainVolumeTarget = 0;                    ///< Latest drain-to volume reported by the DG.
 static U32 dgReservoirDrainVolumeTargetSet = 0;                 ///< Drain-to volume commanded.
 static U32 resUseTimer = 0;                                     ///< used to track time pumping from active reservoir (for volume used calculation).
-static F32 resUseVolumeMl = 0.0;                                  ///< Accumulated volume used from active reservoir.
+static F32 resUseVolumeMl = 0.0;                                ///< Accumulated volume used from active reservoir.
+static BOOL resHasBeenTared[ NUM_OF_DG_RESERVOIRS ];            ///< Flags indicate whether the reservoir has been tared for this treatment.
 
 // ********** private function prototypes **********
 
@@ -104,9 +105,26 @@
     dgTrimmerTempSet = 0.0;
     dgActiveReservoirSet = DG_RESERVOIR_2;
     dgReservoirFillVolumeTargetSet = 0;
-    dgReservoirDrainVolumeTargetSet = 0;
+    dgReservoirDrainVolumeTargetSet = 0;
+    initPreTreatmentReservoirMgmt();
 }
 
+/*********************************************************************//**
+ * @brief
+ * The initPreTreatmentReservoirMgmt function initializes the pre-treatment
+ * reservoir management state machine.
+ * @details Inputs: none
+ * @details Outputs: pre-treatment reservoir management state machine initialized.
+ * @return none
+ *************************************************************************/
+void initPreTreatmentReservoirMgmt( void )
+{
+    // TODO - currentPreTrtResMgmtState = TREATMENT_RESERVOIR_MGMT_START_STATE;
+    resMgmtTimer = 0;
+    resHasBeenTared[ DG_RESERVOIR_1 ] = FALSE;
+    resHasBeenTared[ DG_RESERVOIR_2 ] = FALSE;
+}
+
 /*********************************************************************//**
  * @brief
  * The initTreatmentReservoirMgmt function initializes the treatment reservoir
@@ -123,6 +141,18 @@
     resUseVolumeMl = 0.0;
 }
 
+/*********************************************************************//**
+ * @brief
+ * The execPreTreatmentReservoirMgmt function executes the state machine for the
+ * reservoir management during pre-treatment mode.
+ * @details Inputs: none
+ * @details Outputs: DG reservoirs (drains & fills) managed.
+ * @return none
+ *************************************************************************/
+void execPreTreatmentReservoirMgmt( void )
+{
+}
+
 /*********************************************************************//**
  * @brief
  * The execTreatmentReservoirMgmt function executes the state machine for the
@@ -289,6 +319,20 @@
     return dgActiveReservoirSet;
 }
 
+/*********************************************************************//**
+ * @brief
+ * The getDGInactiveReservoir function gets the currently inactive reservoir.
+ * @details Inputs: dgActiveReservoirSet
+ * @details Outputs: none
+ * @return Currently commanded inactive reservoir.
+ *************************************************************************/
+DG_RESERVOIR_ID_T getDGInactiveReservoir( void )
+{
+    DG_RESERVOIR_ID_T inactiveRes = ( DG_RESERVOIR_2 == dgActiveReservoirSet ? DG_RESERVOIR_1 : DG_RESERVOIR_2 );
+
+    return inactiveRes;
+}
+
 /*********************************************************************//**
  * @brief
  * The getDGPressure function gets the latest pressure reported by the DG
@@ -600,13 +644,18 @@
  * The cmdStartDGDrain function sends a drain command message to the DG.
  * @details Inputs: none
  * @details Outputs: drain command sent to DG.
- * @param drainToVolMl volume (in mL) to drain inactive reservoir to
+ * @param drainToVolMl volume (in mL) to drain inactive reservoir to
  * @return none
  *************************************************************************/
 void cmdStartDGDrain( U32 drainToVolMl )
-{
-    dgReservoirDrainVolumeTargetSet = drainToVolMl;
-    sendDGDrainCommand( drainToVolMl );
+{
+    DRAIN_RESERVOIR_CMD_PAYLOAD_T payload;
+    DG_RESERVOIR_ID_T inactiveRes = getDGInactiveReservoir();
+
+    dgReservoirDrainVolumeTargetSet = drainToVolMl;
+    payload.drainToVolumeML = drainToVolMl;
+    payload.tareLoadCells = ( FALSE == resHasBeenTared[ inactiveRes ] ? TRUE : FALSE );
+    sendDGDrainCommand( &payload );
 }
 
 /*********************************************************************//**
Index: firmware/App/Controllers/DGInterface.h
===================================================================
diff -u -rb01542f8e4ef5a29e9b08fc0d465478de516bf02 -r85ab84d9a0668e1e3976b00eb29e79c38c81b651
--- firmware/App/Controllers/DGInterface.h	(.../DGInterface.h)	(revision b01542f8e4ef5a29e9b08fc0d465478de516bf02)
+++ firmware/App/Controllers/DGInterface.h	(.../DGInterface.h)	(revision 85ab84d9a0668e1e3976b00eb29e79c38c81b651)
@@ -106,15 +106,25 @@
     F32 HtrTrimInternal;
 } DG_TEMPERATURES_T;
 
+/// Payload record structure for a drain reservoir command message.
+typedef struct
+{
+    U32  drainToVolumeML;
+    BOOL tareLoadCells;
+} DRAIN_RESERVOIR_CMD_PAYLOAD_T;
+
 // ********** public function prototypes **********
 
 void initDGInterface( void );
-void initTreatmentReservoirMgmt( void );
-void execTreatmentReservoirMgmt( void );
+void initPreTreatmentReservoirMgmt( void );
+void execPreTreatmentReservoirMgmt( void );
+void initTreatmentReservoirMgmt( void );
+void execTreatmentReservoirMgmt( void );
 
 DG_OP_MODE_T getDGOpMode( void );
 U32 getDGSubMode( void );
 DG_RESERVOIR_ID_T getDGActiveReservoir( void );
+DG_RESERVOIR_ID_T getDGInactiveReservoir( void );
 F32 getDGPressure( DG_PRESSURE_SENSORS_T sensorID );
 U32 getDGROPumpPressureSetPt( void );
 F32 getDGROPumpFlowRateMlMin( void );
Index: firmware/App/Modes/ModeTreatment.h
===================================================================
diff -u -rf6888c7e4e05cb84b11fceb4340458d8af543ce8 -r85ab84d9a0668e1e3976b00eb29e79c38c81b651
--- firmware/App/Modes/ModeTreatment.h	(.../ModeTreatment.h)	(revision f6888c7e4e05cb84b11fceb4340458d8af543ce8)
+++ firmware/App/Modes/ModeTreatment.h	(.../ModeTreatment.h)	(revision 85ab84d9a0668e1e3976b00eb29e79c38c81b651)
@@ -80,7 +80,7 @@
 void initTreatmentMode( void );                                     // initialize this module
 void transitionToTreatmentMode( void );                             // prepares for transition to treatment mode
 U32  execTreatmentMode( void );                                     // execute the treatment mode state machine (call from OperationModes)
-void signalAlarmActionToTreatmentode( ALARM_ACTION_T action );      // execute alarm action as appropriate for Treatment mode
+void signalAlarmActionToTreatmentMode( ALARM_ACTION_T action );     // execute alarm action as appropriate for Treatment mode
 
 TREATMENT_STATE_T getTreatmentState( void );                        // determine the current treatment sub-mode (state)
 
Index: firmware/App/Services/SystemCommMessages.c
===================================================================
diff -u -rc672f41061bcd500d6593655641cb27ce3ae58fc -r85ab84d9a0668e1e3976b00eb29e79c38c81b651
--- firmware/App/Services/SystemCommMessages.c	(.../SystemCommMessages.c)	(revision c672f41061bcd500d6593655641cb27ce3ae58fc)
+++ firmware/App/Services/SystemCommMessages.c	(.../SystemCommMessages.c)	(revision 85ab84d9a0668e1e3976b00eb29e79c38c81b651)
@@ -566,10 +566,12 @@
  * and queues the msg for transmit on the appropriate CAN channel.
  * @details Inputs: none
  * @details Outputs: DG drain command msg constructed and queued.
- * @param drainToVolumeMl volume (in mL) to drain the inactive reservoir to
+ * @param drainToVolumeMl volume (in mL) to drain the inactive reservoir to
+ * @param tareLoadCells set to TRUE if inactive reservoir load cells should be
+ * tared after draining
  * @return TRUE if msg successfully queued for transmit, FALSE if not
  *************************************************************************/
-BOOL sendDGDrainCommand( U32 drainToVolumeMl )
+BOOL sendDGDrainCommand( DRAIN_RESERVOIR_CMD_PAYLOAD_T *payload )
 {
     BOOL result;
     MESSAGE_T msg;
@@ -578,9 +580,9 @@
     // create a message record
     blankMessage( &msg );
     msg.hdr.msgID = MSG_ID_DG_DRAIN_CMD;
-    msg.hdr.payloadLen = sizeof( U32 );
+    msg.hdr.payloadLen = sizeof( DRAIN_RESERVOIR_CMD_PAYLOAD_T );
 
-    memcpy( payloadPtr, &drainToVolumeMl, sizeof( U32 ) );
+    memcpy( payloadPtr, payload, sizeof( DRAIN_RESERVOIR_CMD_PAYLOAD_T ) );
 
     // serialize the message (w/ sync, CRC, and appropriate CAN padding) and add serialized message data to appropriate comm buffer
     result = serializeMessage( msg, COMM_BUFFER_OUT_CAN_HD_2_DG, ACK_REQUIRED );
Index: firmware/App/Services/SystemCommMessages.h
===================================================================
diff -u -rc672f41061bcd500d6593655641cb27ce3ae58fc -r85ab84d9a0668e1e3976b00eb29e79c38c81b651
--- firmware/App/Services/SystemCommMessages.h	(.../SystemCommMessages.h)	(revision c672f41061bcd500d6593655641cb27ce3ae58fc)
+++ firmware/App/Services/SystemCommMessages.h	(.../SystemCommMessages.h)	(revision 85ab84d9a0668e1e3976b00eb29e79c38c81b651)
@@ -163,7 +163,7 @@
 BOOL sendDGFillCommand( U32 fillToVolumeMl );
 
 // MSG_ID_DG_DRAIN_CMD
-BOOL sendDGDrainCommand( U32 drainToVolumeMl );
+BOOL sendDGDrainCommand( DRAIN_RESERVOIR_CMD_PAYLOAD_T *payload );
 
 // MSG_ID_STARTING_STOPPING_TREATMENT_CMD
 BOOL sendDGStartStopCommand( BOOL start );