- Added drainFluidContainer() and getContainerCapacity() helper methods.

src/main/java/net/minecraftforge/fluids/FluidContainerRegistry.java

@@ -226,6 +226,81 @@ public abstract class FluidContainerRegistry
         return null;
     }
 
+    /**
+     * Attempts to empty a full container.
+     * 
+     * @param container
+     *            ItemStack representing the full container.
+     * @return Empty container if successful, otherwise null.
+     */
+    public static ItemStack drainFluidContainer(ItemStack container)
+    {
+        if (container == null)
+        {
+            return null;
+        }
+
+        FluidContainerData data = containerFluidMap.get(new ContainerKey(container));
+        if (data != null)
+        {
+            return data.emptyContainer.copy();
+        }
+
+        return null;
+    }
+
+    /**
+     * Determines the capacity of a full container.
+     * 
+     * @param container
+     *            The full container.
+     * @return The containers capacity, or 0 if the ItemStack does not represent
+     *         a registered container.
+     */
+    public static int getContainerCapacity(ItemStack container)
+    {
+        return getContainerCapacity(null, container);
+    }
+
+    /**
+     * Determines the capacity of a container.
+     * 
+     * @param fluid
+     *            FluidStack containing the type of fluid the capacity should be
+     *            determined for (ignored for full containers).
+     * @param container
+     *            The container (full or empty).
+     * @return The containers capacity, or 0 if the ItemStack does not represent
+     *         a registered container or the FluidStack is not registered with
+     *         the empty container.
+     */
+    public static int getContainerCapacity(FluidStack fluid, ItemStack container)
+    {
+        if (container == null)
+        {
+            return 0;
+        }
+
+        FluidContainerData data = containerFluidMap.get(new ContainerKey(container));
+
+        if (data != null)
+        {
+            return data.fluid.amount;
+        }
+
+        if (fluid != null)
+        {
+            data = filledContainerMap.get(new ContainerKey(container, fluid));
+
+            if (data != null)
+            {
+                return data.fluid.amount;
+            }
+        }
+
+        return 0;
+    }
+
     /**
      * Determines if a container holds a specific fluid.
      */