our hybrid has a really small grey and black tank, but we have used the shower since we usually camp over the weekend with just two of us (humans). This coming fourth of July, we have a site with full hookups, so unlimited water and sewer! That will be fun.
Update: On our trip this past week, we did not have a full hookup site. We also managed to fill the grey and black tanks since we were there for five days. I purchased a 12 gallon rolly-tank at Camping World for about $80, which allowed me to dump the tanks without breaking camp. This was a great purchase. Get the smallest portable tank that is larger than your onboard tank so you don't have to worry about accidentally overfilling it...