There is no drain plug on the transmission. Loosen the pan ( lower pan, not the side valve body cover) bolts leaving 3 corners snug. Place a large drain pan under the transmission. Gently pry down the loose corner of the pan to drain the fluid to pan level.Then continue to remove the pan, draining the remaining fluid as you go.
Bottom or rear of radiator
No, it has one oil drain plug.
On the transmission, right side just above the drain plug. Fill it until it's just below the filler port
You can find the 1991 Buick Skylark radiator drain plug on the bottom of the radiator. The radiator drain plug will be in the center of the radiator bottom.
Rear end of the engine - front end of the transmission
There probably isn't one. Most U.S. cars require you to drop the transmission pan to drain the fluid, which you'd need to do to change the filter anyway. Just get the biggest pan you can find and resign yourself to taking a transmission fluid bath.
Its a drain plug incase your car ever gets flooded.
There is a fill plug but to drain it you must take off differential cover and replace gasket onto clean mating surfaces.
To drain the oil on a 1991 Chevy S10 Blazer, located the oil pan drain plug. Use a wrench to remove the plug and the oil will flow into the receptacle you have provided.
Drivers side, about midway up the side of the transmission.
Put the car on a lift and find the transmission fluid drain plug (which is usually close to the passenger side front wheel). Unscrew the plug and let the fluid drain, then replace the plug and let the car down. Pop the hood and look just behind the radiator for a small dipstick, that's the tranny dipstick. Pull it out and use a funnel to re-fill it with fluid.
Look at the rear or side of the oil pan