Your 2000 Prizm has a GM/Delco A/C system unlike the Corollas. The Delco A/C compressor is a V-5 variable displacement compressor which are known to leak from the compressor shaft seal after many miles of use. This may or may not be where your leak is, but it is a known area of trouble. When charging, try applying a soapy water mix around suspected areas and look for bubbbles. Or you can add dye to the system when charging to help identify the area of the leak. Also, with a leak that severe, you should see signs of compressor oil at the point of the leak. Another option is to buy, rent, or borrow an electronic refrigerant detector to help find the leak. Check around the compressor shaft seal first. I had to change the compressor in my '99 Prizm because of the bad shaft seal. Got a great deal on ebay on a new Delco compressor. Consider also changing out the accumulator and orifice tube at the same time. You must pull a vacuum of 29 to 30" with a vacuum pump after the system is reassembled, and before adding the refrigerant to remove all moisture and air from the system. Also, if you can't maintain 29 to 30" of vacuum in the repaired system before adding refrigerant, you still have a leak somewhere.