Chain Completable into Observable flow

Suppose you want to insert a Completable in your Observable chain, such as for each emitted element, there is a completable that runs and blocks until it completes, what option would you choose? (here the Completable.complete() is just to make an example)

1. .flatMap { Completable.complete().andThen(Observable.just(it)) }

2. .doOnNext { Completable.complete().blockingAwait() }

3. something else?