If that won't work, do you have any state parks with onsite campgrounds near by? Do they have a ranger on duty year round?
Or install a larger waste water tank in your unit and another in a truck bed. Use a small sludge pump, or a shop vac to pump your gray water to the truck tank once a month and haul your water to the nearest dump site. Be careful if you spill any of the water during transfer it may take two maybe 3 months to make a trip worthwhile. But I have no idea how you'd keep the water from freezing in the winter months while in route to dump it.
And don't be surprised to find some jerk in an office that will want you to get some special waste haulers permit or license.
By the way and you most likely know this, but you can never dump scrap food debris especially meats, beans, cheese, any kind of grease and noodles, in your sink system. If you do it will clog up your drain, on your gray water tank in a heartbeat. We use paper towels to wipe out all of our pans before we wash them.
One other thought, our health department will allow us to put used frying oil into it's original container in our dumpster and send it to the landfill. Will yours allow that? If so why can't you put your gray water into five gallon buckets and send it to a landfill? It's just dish washing water right not from a toilet?
<message edited by Dr of BBQ on Mon, 10/24/11 5:28 PM>