Edit in JSFiddle

// setup

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

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