Edit in JSFiddle

// setup
function finder(records, cb) {
    setTimeout(function () {
        records.push(3, 4);
        cb(null, records);
    }, 500);
}
function processor(records, cb) {
    setTimeout(function () {
        records.push(5, 6);
        cb(null, records);
    }, 500);
}

async.waterfall([
    function(cb){
        finder([1, 2], cb);
    },
    processor
    ,
    function(records, cb) {
        alert(records);
    }
]);