Drain pipe DN32 to DN40 but seal inside

Hello.
I have an existing floor drain (see sketch), it is an HL541. I want to seal another pipe into the drain opening of the floor drain, e.g. a DN32 pipe with an elbow.
But how?
The inner diameter of the drain opening is about 36mm, like a DN40 pipe, the outer diameter of a DN32 pipe is exactly 32mm.
I need a gasket between them.
Is there a suitable socket gasket for this? The socket gaskets I have seen and tested so far were all too thick; I couldn’t get them into the drain opening.
Or rather, I could get them in, but then the DN32 pipe no longer fit inside... A standard 40/32 socket gasket is not meant for this, I know, it has an outer diameter of at least 40mm.
I need a 36/32 socket gasket, is there such a thing?
Does anyone have an idea how I can seal this well? So that it’s also removable again, I don’t want to glue it because it must be removable.
PS: The pipe I want to seal into the floor drain does not necessarily have to be DN32. It can also be a DN40 or something completely different.
Maybe someone has an idea with another pipe?
Thanks Matthias

Modify EPDM conical hollow plugs slightly, glue them to the DN32 pipe, and then press them into the larger DN40. It should hold and is removable.
Or an EPDM rubber sleeve.
Just enter it in the search engine on the internet, there are solutions for such things.

Modify EPDM conical hollow plugs a bit, stick them firmly onto the DN32 pipe and then push them into the larger DN40. It should hold and is reversible.
Or an EPDM rubber sleeve.
Just try entering it into a search engine online, there are solutions for such things.

Thanks already, yes, it actually sounds quite promising.

My first sketch was just a schematic sketch so that one can understand more quickly what I want to do.
It is not really a simple 40mm pipe; it is the outlet spigot of a floor drain which is shaped like a 40mm pipe.
And I have to somehow seal another pipe inside the outlet spigot of the floor drain.
The outlet spigot of the floor drain has an inner diameter of about 36mm.
And finally, I want to connect a freestanding or semi-freestanding bathtub (wall-mounted bathtub) with a drain into the floor drain (actually it was a shower drain).

Here is a new sketch again with more details. Or rather how it really is...
I somehow have to get a connection from the flexible hose coming from the bathtub trap tight into the floor drain.
It's not correct like this, I know. And I am also aware that if I come from the bathtub with a 40mm pipe and reduce to DN32, I create a weak point where blockages are preprogrammed.
But since it is a semi-freestanding bathtub, I can also relatively easily move it forward again to fix any possible blockage.
What I am not allowed to do (because it is a rental apartment) is to chip open the floor and install a new connection.
Thanks for your tips. Matthias.