I found this hose on Amazon.
Notice that the two couplers are different. That would allow you to simply extend your regular hose. Use two if you have to. Otherwise, it'd be a matter of finding an adapter to connect two regular hoses, and so far I haven't seen one that didn't require you to first remove the existing couplers. Such a coupling follows.
This solution is much more expensive, but you might be able to borrow one. Dump into a portable tank and drain the tank at the dump station.
Two of us can go about 10 days using campground showers and the toilets during the day. But that takes practice. If your crew isn't used to conserving on waste water, you won't go seven days.