Because he ate the tube as well, you need to give your vet a call. The plastic is going to be hard to pass.
You can get the clobetasol out of his system by giving him 3 tbsp of peroxide by mouth. BUT I would not do this if he ate the tube because he could choke on the parts coming back up.
If you don't get the tube parts out, he could end up with an obstruction of the bowels and this can be life threatening.
I hate that you are going through this.
Give your vet or an after hours clinic a call. They will let you know if it's urgent that you come in.
I hope this helps!
Good luck!