Let me start by saying we don’t use our sink in the A-liner. It is small and since we live in a climate the freezes, we don’t find it worth the extra work it takes to drain in for the off-season. For clean water, we look elsewhere.
In the past, we would stock up on gallon-sized jugs of water from Costco before camping to ensure that we would have clean water for just about everything, from filling the dogs’ water bowls to cleaning dishes. These took up considerable space in the vehicle and also created bulky trash. But you need clean water.