diff --git a/src/sink.test.ts b/src/sink.test.ts
index 96ebe38..0d8a942 100644
--- a/src/sink.test.ts
+++ b/src/sink.test.ts
@@ -4,19 +4,29 @@ const foo = new Updux<number>({
   initial: 0,
   mutations: {
     doIt: () => (state: number) => {
-      console.log(state);
       return state + 1;
     },
+    doTheThing: () => (state: number) => {
+      return state + 3;
+    },
   },
 });
 
 const bar = new Updux<{foo: number}>({
   subduxes: {foo},
-  mutations: {
-    doIt: () => (state: any) => state,
-  },
 });
 
+bar.addMutation(
+  foo.actions.doTheThing,
+  (_, action) => state => {
+    return {
+      ...state,
+      baz: bar.subduxUpreducer(action)(state),
+    };
+  },
+  true,
+);
+
 bar.addMutation(
   foo.actions.doIt,
   () => (state: any) => ({...state, bar: 'yay'}),
@@ -37,3 +47,10 @@ test('sink mutations', () => {
     bar: 'yay',
   });
 });
+
+test('sink mutation and subduxUpreducer', () => {
+  expect(bar.reducer(undefined, bar.actions.doTheThing())).toEqual({
+    foo: 0,
+    baz: {foo: 3},
+  });
+});
diff --git a/src/updux.ts b/src/updux.ts
index 76a268a..6443db2 100644
--- a/src/updux.ts
+++ b/src/updux.ts
@@ -188,6 +188,27 @@ export class Updux<S = any> {
     return buildMutations(this.localMutations, this.subduxes);
   }
 
+  /**
+   * Returns the upreducer made of the merge of all sudbuxes reducers, without
+   * the local mutations. Useful, for example, for sink mutations.
+   * @example
+   * ```
+   * import todo from './todo'; // updux for a single todo
+   * import Updux from 'updux';
+   * import u from 'updeep';
+   *
+   * const todos = new Updux({ initial: [], subduxes: { '*': todo } });
+   * todos.addMutation(
+   *     todo.actions.done,
+   *     ({todo_id},action) => u.map( u.if( u.is('id',todo_id) ), todos.subduxUpreducer(action) )
+   *     true
+   * );
+   * ```
+   */
+  @computed get subduxUpreducer() {
+    return buildUpreducer(this.initial, buildMutations({}, this.subduxes));
+  }
+
   /**
    * Same as doing
    *
@@ -248,7 +269,8 @@ export class Updux<S = any> {
    * If a local mutation was already associated to the action,
    * it will be replaced by the new one.
    * @param isSink
-   * If `true`, disables the subduxes mutations for this action.
+   * If `true`, disables the subduxes mutations for this action. To
+   * conditionally run the subduxes mutations, check out [[subduxUpreducer]].
    * @example
    * ```
    * updux.addMutation( add, inc => state => state + inc );