There have been 3 types of rectal anesthesia.
Ether in Oil. The ether dissolves in the oil and is less irritating, however the bowel will absorb the ether, and once the blood level gets high enough, the patient is unconscious.
At least into the late 1960's Abbott Laboratories made a prefilled syringe with Sodium Thiopental (Penothatl®) intended
for rectal use.
Up until about 1960 there was a product called Avertin, Tribromoethanol dissolved in Tert Amyl Alcohol, It provided
'basal' anesthesia. In other words it kept the patient asleep, but didn't do much to control pain, so once the patient was unconscious, other anesthetics could be utilized. Tribomoethanol is a first cousin to Chloral Hydrate (that may still be
available in suppository form). The body very rapidly breaks down Chloral Hydrate into Trichlorethanol, which is believed to be the active drug. Avertin went out of style because to be blunt, it was PIA to use. Tribromoethanol
is still used as an anesthetic for rodents. Tribromoethanol is not a restricted chemical, but it is quite expensive.
I believe Midazolam and Lorazepam (benzodiazapines) are both given rectally sometimes for sedation in very young children.