Try Annapolis Harbor Boat Yard (formerly Steve's Yacht Repair). They are in Eastport, right alongside the Chart House Restaurant. Their address is 326 First Street, Annapolis (410) 268-0092. Kevin or Tom. They aren't GB specialists, but they do an awful lot of marine plumbing and sanitation work. They have their own docks, where you can tie up. If you're in the water in the City Dock area, look to your left, toward the Chart House; then look for the large white painting tent, to the left of the Chart House. That's their place.