diff --git a/timely/src/dataflow/channels/mod.rs b/timely/src/dataflow/channels/mod.rs
index 7d174f083..c3828a6ca 100644
--- a/timely/src/dataflow/channels/mod.rs
+++ b/timely/src/dataflow/channels/mod.rs
@@ -47,26 +47,13 @@ impl<T, D> Message<T, D> {
     }
 
     /// Forms a message, and pushes contents at `pusher`. Replaces `buffer` with what the pusher
-    /// leaves in place, or a new `Vec`. Note that the returned vector is always initialized with
-    /// a capacity of [Self::default_length] elements.
+    /// leaves in place, or a new `Vec`. If the returned vector has a different capacity than the
+    /// default, it will be replaced with an empty vector.
+    ///
+    /// Clients are responsible to ensure that their buffers are allocated before reusing them.
     #[inline]
     pub fn push_at<P: Push<Bundle<T, D>>>(buffer: &mut Vec<D>, time: T, pusher: &mut P) {
 
-        Self::push_at_no_allocation(buffer, time, pusher);
-
-        // Allocate a default buffer to avoid oddly sized or empty buffers
-        if buffer.capacity() != Self::default_length() {
-            *buffer = Vec::with_capacity(Self::default_length());
-        }
-    }
-
-    /// Forms a message, and pushes contents at `pusher`. Replaces `buffer` with what the pusher
-    /// leaves in place, or a new empty `Vec`. If the pusher leaves a vector with a capacity larger
-    /// than [Self::default_length], the vector is initialized with a new vector with
-    /// [Self::default_length] capacity.
-    #[inline]
-    pub fn push_at_no_allocation<P: Push<Bundle<T, D>>>(buffer: &mut Vec<D>, time: T, pusher: &mut P) {
-
         let data = ::std::mem::take(buffer);
         let message = Message::new(time, data, 0, 0);
         let mut bundle = Some(Bundle::from_typed(message));
@@ -80,9 +67,9 @@ impl<T, D> Message<T, D> {
             }
         }
 
-        // Avoid memory leaks by buffers growing out of bounds
-        if buffer.capacity() > Self::default_length() {
-            *buffer = Vec::with_capacity(Self::default_length());
+        // Avoid oddly-sized buffers
+        if std::mem::size_of::<D>() > 0 && buffer.capacity() != Self::default_length() {
+            *buffer = Default::default();
         }
     }
 }
diff --git a/timely/src/dataflow/channels/pushers/buffer.rs b/timely/src/dataflow/channels/pushers/buffer.rs
index 288d5ff88..47663c308 100644
--- a/timely/src/dataflow/channels/pushers/buffer.rs
+++ b/timely/src/dataflow/channels/pushers/buffer.rs
@@ -23,7 +23,7 @@ impl<T, D, P: Push<Bundle<T, D>>> Buffer<T, D, P> where T: Eq+Clone {
     pub fn new(pusher: P) -> Buffer<T, D, P> {
         Buffer {
             time: None,
-            buffer: Vec::with_capacity(Message::<T, D>::default_length()),
+            buffer: Default::default(),
             pusher,
         }
     }
@@ -65,8 +65,12 @@ impl<T, D, P: Push<Bundle<T, D>>> Buffer<T, D, P> where T: Eq+Clone {
 
     // internal method for use by `Session`.
     fn give(&mut self, data: D) {
+        // Ensure default capacity
+        if self.buffer.capacity() < Message::<T, D>::default_length() {
+            let to_reserve = Message::<T, D>::default_length() - self.buffer.capacity();
+            self.buffer.reserve(to_reserve);
+        }
         self.buffer.push(data);
-        // assert!(self.buffer.capacity() == Message::<O::Data>::default_length());
         if self.buffer.len() == self.buffer.capacity() {
             self.flush();
         }
diff --git a/timely/src/dataflow/channels/pushers/exchange.rs b/timely/src/dataflow/channels/pushers/exchange.rs
index 21c781cff..de613d2cc 100644
--- a/timely/src/dataflow/channels/pushers/exchange.rs
+++ b/timely/src/dataflow/channels/pushers/exchange.rs
@@ -31,7 +31,7 @@ impl<T: Clone, D, P: Push<Bundle<T, D>>, H: FnMut(&T, &D)->u64>  Exchange<T, D,
     fn flush(&mut self, index: usize) {
         if !self.buffers[index].is_empty() {
             if let Some(ref time) = self.current {
-                Message::push_at_no_allocation(&mut self.buffers[index], time.clone(), &mut self.pushers[index]);
+                Message::push_at(&mut self.buffers[index], time.clone(), &mut self.pushers[index]);
             }
         }
     }
diff --git a/timely/src/dataflow/channels/pushers/tee.rs b/timely/src/dataflow/channels/pushers/tee.rs
index f5e3915ea..fd5e22289 100644
--- a/timely/src/dataflow/channels/pushers/tee.rs
+++ b/timely/src/dataflow/channels/pushers/tee.rs
@@ -23,6 +23,10 @@ impl<T: Data, D: Data> Push<Bundle<T, D>> for Tee<T, D> {
         let mut pushers = self.shared.borrow_mut();
         if let Some(message) = message {
             for index in 1..pushers.len() {
+                // Ensure default capacity
+                if self.buffer.capacity() != Message::<T, D>::default_length() {
+                    self.buffer = Vec::with_capacity(Message::<T, D>::default_length());
+                }
                 self.buffer.extend_from_slice(&message.data);
                 Message::push_at(&mut self.buffer, message.time.clone(), &mut pushers[index-1]);
             }
@@ -44,7 +48,7 @@ impl<T, D> Tee<T, D> {
     pub fn new() -> (Tee<T, D>, TeeHelper<T, D>) {
         let shared = Rc::new(RefCell::new(Vec::new()));
         let port = Tee {
-            buffer: Vec::with_capacity(Message::<T, D>::default_length()),
+            buffer: Default::default(),
             shared: shared.clone(),
         };
 
@@ -55,7 +59,7 @@ impl<T, D> Tee<T, D> {
 impl<T, D> Clone for Tee<T, D> {
     fn clone(&self) -> Tee<T, D> {
         Tee {
-            buffer: Vec::with_capacity(self.buffer.capacity()),
+            buffer: Default::default(),
             shared: self.shared.clone(),
         }
     }
diff --git a/timely/src/dataflow/operators/input.rs b/timely/src/dataflow/operators/input.rs
index 11d02896d..94367b6cf 100644
--- a/timely/src/dataflow/operators/input.rs
+++ b/timely/src/dataflow/operators/input.rs
@@ -212,8 +212,8 @@ impl<T:Timestamp, D: Data> Handle<T, D> {
             activate: Vec::new(),
             progress: Vec::new(),
             pushers: Vec::new(),
-            buffer1: Vec::with_capacity(Message::<T, D>::default_length()),
-            buffer2: Vec::with_capacity(Message::<T, D>::default_length()),
+            buffer1: Default::default(),
+            buffer2: Default::default(),
             now_at: T::minimum(),
         }
     }
@@ -258,7 +258,7 @@ impl<T:Timestamp, D: Data> Handle<T, D> {
         progress: Rc<RefCell<ChangeBatch<T>>>
     ) {
         // flush current contents, so new registrant does not see existing data.
-        if !self.buffer1.is_empty() { self.flush(); }
+        self.flush();
 
         // we need to produce an appropriate update to the capabilities for `progress`, in case a
         // user has decided to drive the handle around a bit before registering it.
@@ -272,8 +272,15 @@ impl<T:Timestamp, D: Data> Handle<T, D> {
     // flushes our buffer at each of the destinations. there can be more than one; clone if needed.
     #[inline(never)]
     fn flush(&mut self) {
+        if self.buffer1.is_empty() {
+            return;
+        }
         for index in 0 .. self.pushers.len() {
             if index < self.pushers.len() - 1 {
+                // Ensure default capacity
+                if self.buffer2.capacity() != Message::<T, D>::default_length() {
+                    self.buffer2 = Vec::with_capacity(Message::<T, D>::default_length());
+                }
                 self.buffer2.extend_from_slice(&self.buffer1[..]);
                 Message::push_at(&mut self.buffer2, self.now_at.clone(), &mut self.pushers[index]);
                 debug_assert!(self.buffer2.is_empty());
@@ -288,7 +295,7 @@ impl<T:Timestamp, D: Data> Handle<T, D> {
 
     // closes the current epoch, flushing if needed, shutting if needed, and updating the frontier.
     fn close_epoch(&mut self) {
-        if !self.buffer1.is_empty() { self.flush(); }
+        self.flush();
         for pusher in self.pushers.iter_mut() {
             pusher.done();
         }
@@ -304,7 +311,11 @@ impl<T:Timestamp, D: Data> Handle<T, D> {
     #[inline]
     /// Sends one record into the corresponding timely dataflow `Stream`, at the current epoch.
     pub fn send(&mut self, data: D) {
-        // assert!(self.buffer1.capacity() == Message::<T, D>::default_length());
+        // Ensure default capacity
+        if self.buffer1.capacity() < Message::<T, D>::default_length() {
+            let to_reserve = Message::<T, D>::default_length() - self.buffer1.capacity();
+            self.buffer1.reserve(to_reserve);
+        }
         self.buffer1.push(data);
         if self.buffer1.len() == self.buffer1.capacity() {
             self.flush();
@@ -318,21 +329,12 @@ impl<T:Timestamp, D: Data> Handle<T, D> {
 
         if !buffer.is_empty() {
             // flush buffered elements to ensure local fifo.
-            if !self.buffer1.is_empty() { self.flush(); }
-
-            // push buffer (or clone of buffer) at each destination.
-            for index in 0 .. self.pushers.len() {
-                if index < self.pushers.len() - 1 {
-                    self.buffer2.extend_from_slice(&buffer[..]);
-                    Message::push_at(&mut self.buffer2, self.now_at.clone(), &mut self.pushers[index]);
-                    assert!(self.buffer2.is_empty());
-                }
-                else {
-                    Message::push_at(buffer, self.now_at.clone(), &mut self.pushers[index]);
-                    assert!(buffer.is_empty());
-                }
-            }
-            buffer.clear();
+            self.flush();
+
+            // flush sends and clears the contents of self.buffer1, re-use by swapping buffers
+            ::std::mem::swap(&mut self.buffer1, buffer);
+            self.flush();
+            ::std::mem::swap(&mut self.buffer1, buffer);
         }
     }