It is strange that modern Greeks seem to have the lost skills they had 2000 years ago! Greek Plumbing is a surprise to most first time visitors but as said above it is surprising how quickly one adjusts. In fact the main reason for this, apart from the small pipes is most houses have soak away/pittal tank sewerage systems which would very quickly get clogged with paper. Some hotels like the Gelina and St Georges Bay in Acharavi have their own sewerage systems but still cannot filter paper(etc!). Corfu town now has a mains sewerage system but many houses still do not have big enough pipes to cope with large amounts of paper.
Sorry, like many things change comes slowly, but it is coming!
Dont let it put you off. Greece in general and Corfu in particular are wonderful places for a holiday and all the plus points far outweigh the minus.