ᐅ Empty conduits leading outside – What is the best way to seal them airtight?

Hello experts,
I am building a KfW efficiency house that requires a blower door test.
I have several empty conduits for roller shutters/blinds leading outside, but only one cable has been installed in them.
How can I make these airtight?
Thanks and good luck
Christian

Is it supposed to be watertight only for testing purposes? How about using tape?

It should already be a reasonable solution and also watertight afterward...

As a layperson, I would use well foam.

There are blind plugs/sealing plugs/closure plugs/stop plugs available from Kaiser, Fränkische, Proclima, etc., which have a membrane that can be pierced. This works quite well for a conduit.