It's just the wife and me, and our TT has a 30 gallon black tank and 60 gallon grey tank. We don't use the campground facilities, so all of our water is used in the TT.
Our black tank usually gets to around 2/3 full in 4 days, although we flush with plenty of water to help the tank flush properly when we dump. I think we could easily go 6+ days if we cut back on the flush water, although I'd flush the black tank well when dumping.
The grey water tank will last 4-6 days, showering using Navy method. We also adjust our usage habits based on how long we're going to stay somewhere. If we're only staying somewhere for 2 nights, we tend to use more water when showering, washing dishes, etc.
Couple of tips to save water:
* Navy method for showering (huge savings here)
* Minimize washing dishes (huge savings here also) by using paper plates and plastic cups. I'll wash dishes outside if we're staying somewhere 5+ days.
* Buy a small 1 gallon bucket and use that to hold water for certain tasks, then throw it outside. For example, when first turning on the shower to get hot water, I run the water into that bucket until the water is hot, then the bucket gets drained outside after the shower. In my TT, that saves around 1/3 gallon each shower.
