On one of our early
Scamp trips to a park with hookups we had been using water like we do at home. The last day of our trip, the sink started to back up.
That was the only indication we've ever gotten that our grey tank is full; ever since then we've been much more careful with our water usage. It takes a little practice, but the two of us can easily go a week without having to dump the grey tank.
We have a privacy/shower closet, but do not shower in our
Scamp, not even when we have full hookups. Not only does showering use (literally) buckets of water, the Scamp's 6-gallon water heater wouldn't support a long shower, and showering makes for a wet toilet and damp trailer. We prefer to use camp showers or do a sponge bath and wash our hair at the sink. That keeps water consumption to just one quart of water, which is very handy when we're
boondocking.
When we boondock, we know that we can refill our (upgraded) 17 gallon fresh tank using jerry cans once before having to worry that our grey tank might fill to overflowing. (Our grey tank won't hold 34 gallons, but it never quite fills all the way, and some of the water goes to the black tank when we flush our toilets.)
I'm sure you'll both learn to cope. It didn't take us all that long to do so, and now we hardly think about it at all.