Caravanning without facilities

We are new to caravanning and have been invited to an event taking place in a park rather than a caravan site. There are no facilities there other than toilets / fresh water. After several days use of the caravan what do caravanners do about the chemical toilet? There will be nowhere to empty it. Is it safe to drive along without emptying it first? If not what do other people do? Also there is no electric supply and we are wondering how long we will be able to use the lights in the caravan. We have a 115amp leisure battery. Any help or advice would be very welcome. Thanks.