Instead of replay, use a connectable observable

connected_observable_demo.md

    public static void main(String[] args) {
        ConnectableObservable<String> producer = Observable.just("Hello World 100").publish();

        Observable<String> hi = producer.map(String::toUpperCase);
        Observable<String> lo = producer.map(String::toLowerCase);
        Observable<String> no100 = producer.filter(s -> s.contains("100")).map(s -> s.replace("100", "1000"));

        Observable<String> combined = Observable.merge(lo, hi, no100);
        combined.subscribe(System.out::println);

        // Only emit from the producer when connect() is called.
        producer.connect();
    }