plumbing into an 18th Century house, perhaps some of the solutions we found for the Hall Christy house can be of help.
When we found the house, there was only one corner that had plumbing in it. We tried to limit our modern solutions to that corner with the kitchen and powder room below and the upstairs bathroom above. This was nearly 30 years ago so we had to use our own ingenuity to come up with what has become more readily available on the market.
The Hall Christy house did not tend to a primitive look as there is some rather sophisticated paneling and wood work throughout, so our choices were more formal, although they readily could be adapted to a primitive style of cabinetry. And, yes, we love the wonderful stone baths we encounter in Europe, but did not think them appropriate for an American farm house nor, quite frankly, did we have the room. As with most 18th Century houses, bathroom spaces are not large.
We wanted the upstairs bathroom to appear as an 18th Century dressing room. As you can see from the pictures, what appears to be a corner cupboard is really the shower. The cupboard across from the sink (corian sunk into a Baker furniture Queen Anne cherry sideboard) opens up to my favorite thing in the bathroom - a jacuzzi tub!
Our biggest challenge came when we wanted to add for marketing purposes a second Jack and Jill bathroom upstairs between the two guest bedrooms. Our house is built in the Hudson Valley Dutch frame vernacular so that the ceilings below are the floors above - no place for plumbing. The upstairs ceiling height is also too low to allow for putting a higher floor in the bathroom area to make a space for the plumbing. One of the bedrooms was in the lean-to section of our saltbox with the floor level being two feet lower than the non-lean-to section of the second floor.
Magic? No. We simply put the drain into the adjacent bedroom where there was the two foot drop. The soil pipe for all the bathroom fitures is in the space borrowed from the bedroom. The soil pipe then goes straight down through another chase created by the lean-to addition directly to the basement and soil pipe leading outside to the septic system.
I hope this helps you all to get your creative juices going for your own solutions. This hiding of the modern fitures has an added benefit of providing hours of delight for all the children who visit. They run in asking if they can go through the house to see what's behind all the doors!