Hello. What is the correct way to drain a subscription if a dispatcher created it?

For example, this is how I create a subscription:

val subscription = dispatcher.subscribe("my-subject") { message ->
    println("Received message: ${message.data}")
}

Then, when I want to unsubscribe, I should do the following:

// subscription.unsubscribe() - not correct way, throws IllegalStateException
dispatcher.unsubscribe(subscription) // correct way 

But how to drain a subscription?
There is no method like dispatcher.drain(subscription).

As far as I understand, all the difference between subsctiption.unsubscribe() and dispatcher.unsubscribe(subsctiption) is that the second method has the following code:

// Grab the NatsSubscription to verify we weren't given a different manager's subscription.
NatsSubscription sub = this.subscriptionsWithHandlers.get(ns.getSID());

Which is not present in subscription.drain()

So how to drain a subscription correctly if Dispatcher created it?
Thanks!