How to add a gulp task to an existing watch task?

Question

I want to add Browser Sync to the gulpfile.js, and got so far as below.

It is a Drupal 8 site on MAMP / apache 80.

I have this working script when I run gulp runbsync. I would like to add it to gulp watch.

I have tried various methods to include the task inside of gulp.task('watch:css', all of which simply failed.

  var browserSync = require('browser-sync').create(),
      reload = browserSync.reload;

    //define task
    gulp.task('bsync', function () {
        //spin up dev server
        browserSync.init({
          proxy: "dev.sitename.local",
          hostname: "dev.sitename.local",
          port: 3000, //even if apache is running on 80 or something else
        });

        //when css files change, reload browserSync 
        gulp.watch('./css/*.css').on('change', function () {
            browserSync.reload();
        });

    });

    //call task with 'gulp runbsync'
    gulp.task('runbsync', ['bsync']);

The watch parts are:

// The default task.
gulp.task('default', ['build']);

// Build everything.
gulp.task('build', ['sass', 'drush:cc', 'lint']);

// Default watch task.
// @todo needs to add a javascript watch task.
gulp.task('watch', ['watch:css']);

// Watch for changes for scss files and rebuild.
gulp.task('watch:css', ['sass', 'drush:cc', 'lint:sass'], function () {
  return gulp.watch(options.theme.scss + '**/*.scss', options.gulpWatchOptions, ['sass', 'drush:cc', 'lint:sass']);
});

I dont know if other parts of the file are nessesary so I left them out here and made a repo (you can even send a pull request)

https://github.com/petergus/D8-zurb-foundation-gulp-browsersync/blob/master/gulpfile.js