While reading up on Alde Heating system can across this info. As far as I can remember it was in relation to motor homes but I suspect system should be similar. Might give you an idea what to look for.
The anti freeze drain on our Lunar Clubman is in the middle of the caravan right at the back. There is a tube dropping with a brass bung held in place with a spring clip.
A day of all things motorhome and campervan. The show is held both in the main indoor arena and across the grounds. Catering, hot drinks and food options are available. Easy access to the site and free parking included. Win one of five pairs of day tickets