How do i drain 2004 lasabre air conditioning drain?

If you're asking how to change it, the fuel tank has to be removed.

Clean out the drain hole in the evaporator case. You can get to it from under the truck.

your air conditioning drain is probably stopped up.the drain is located on the passenger side along the firewall.

I usually unclog them using a puff of compressed air. The crud that plugs them is pretty soft and generally is quite easy to blow out. It may plug up again a time or two until the crud works itself out but usually once the drain is finally clear it will stay open for quite a while.

A/C condenses water out of the air. That water is supposed to drain through a hose that leads from the A/C heater unit. If it gets plugged, the water will stand and eventually molds.
You need to find the drain tube and clear it. If you can find the tube, get some mechanics wire (thinner than a coat hanger), bend the end into an eye, so it will NOT catch on anything, then clean out the tube.

If you can, run the air conditioning for a while to ensure that some water exists. This can help find the tube if it leaks a little, and will definitely help if you do clear the plug, since it will begin to drain when you clear the plug.

did you find where the drain out put is in the air conditioning assembly box located on the firewall. It should be a clear or black hose coming off of the air conditioning assembly. If you use a coat hanger or a piece of wire about the same diameter of a wire coat hanger and use the wire and stick it up the hose to clear the debris out of the way(probably leaves and such pretty common).

clogged drain tube. get a small piece of wire and locate the tube from underneath the vehicle. carefully poke the wire into the tube several times to break up any blockage.

more than likely it's a vacuum problem, look for connections whether off or hoses that need to be replaced

it has disc brakes front and rear.