The interior of the Graves' house is the same set used for The Brady Bunch (1969) (with just a few minor changes). The exterior shots are from a different house, however.
This Mannix aired 2/7/1970 if viewers tuned into the Brady Bunch 2/6/70 they saw Alice sprain her leg in the same house (set) where Sylvia lived. Although decked out with a bar in the dinning room and bits of different furniture you cannot escape the iconic staircase, classic entryway and a glimpse of the swivel kitchen dining chairs in the kitchen where all the Bradys ate breakfast.
The bar set where Mannix meets Sylvia is the same one used for Mannix's interior office.
As Mannix enters the Graves' house about the 5 minute mark, the music played is "Cinnamon" from the Mission Impossible soundtrack. Bruce Geller wrote, produced, and directed both series.