Site should & DO drain all water from pipes & toilets, any water that expands will freeze & blow the plastic joints.
Don't use salt as it expands, overflows the bowls & makes a mess.
Use cat litter which keeps working throughout the closed season, is also far cheaper.
Don't close curtains up which some owners do, but remove & take home to clean.
All bed mattresses & sofas etc must be away from walls, don't cover these with plastic which some owners do as this ends up with mould being introduced.
Put mothballs down on airvents as this stops vermin (farmers put them in tractors etc to keep out mice etc..).
Pay the site to do draindown then if anything goes wrong they are responsible for fixing.
Do it yourself can result in the cost of a new boiler etc..
Dave & Chris