I would also just keep an eye on the tank level sensors, and conserve water as much as possible. Who wants to stand in line for a shower, and I guess they are not free. The pump out should be less than $40 but who knows?
What I might recommend is using the black tank some more. Like do dishes in a dishpan, and save the gallon or so of water in a used milk jug, and use that as flush water. Any excess water can go into the toilet.
I have a tub/shower, and can plug the tub. Then I can use the dishpan to scoop out about 2/3 of the shower water, and either refill the flush jug, or pour it directly into the toilet, and avoid filling the grey tank.
If you get desperate, you can also fill a 5 gallon pail with shower or sink water, then dispose of that at the nearest toilet.
These are great tips for both dry camping in the forest service campgrounds, and at a NASCAR race, where dumping the grey water will get you fined and kicked out too!
Have fun at the race. Bring along towles, someone will say "I want to put a chair on your roof" and you will be thinking a towel would be nice to have under the chair to avoid roof damage. Or let them sit on the towel on the roof, no chairs at all.
Fred.
