Alternate means of waterproofing carbon seat post interface, revisited

My main ride has a carbon fiber sleeve in the seat tube, at the clamping
area. The seat post itself is aluminum, but with a CF sleeve, grease isn't
required or recommended.

I'm trying to keep water from entering the frame at that interface, and will
install a fender. But I thought there was a post here revealing some
alternative to grease in waterproofing frames and CF seat posts--some sort
of tape? Searched via Google Group but came up snake eyes. Maybe my mind is
playing tricks on me.

The wax ring used for installing a toilet makes me consider a bit of beeswax
spread across the notch at the seat clamp, plus a little around the top of
the seat tube ...

Thanks,

Brian Ray