Leak in the front/middle of the undercarriage

under can be anywhere for leak --passenger rear look at holding tank and hoses --towards middle rear heater core or hoses --towards front radiator or hoses

The a/c condensor is up front and mounted low you could have ruptured the line. It will stop after it lost all its pressure. Also there is a vacuum plastic can(tank) mounted under splash shield also.

On most of these heat shields, they are bolted on, so look for the nuts, then there are some that are attached to the catalytic converter and welded on but you should be able to see if there is a leak, due to the lines wouldn't be so close, but these are known to leak in the area you are talking about like Dodges pick up trucks and vans, on how they run the brake lines up under the gas tank, and are known to rust and leak so more or likely you have a leak

If it looks like clear water, and it is leaking when the ac is running, its condensation water from the inside of the car.
Totally normal.

Check water pump and freeze plugs.

Hello, You really need to look under the Vehicle to see what is leaking. Best if you can put it inside with several newspapers under it. Then if it is a slow leak you will be able to look directly above the drip stain.
You have several things which could leak. There is a water draintube from the Air Conditioning ducts and it is normal and harmless for this tube to drain. Look at the color of what fluid is draining. Red usually means transmission fluid. There are cooling lines running from the Trans to the radiator. They can leak as well as the trans gasket.
If you have a 4wheel drive, the transfer case can also leak. Photos for the undercarriage are few and far between. Try a Web Browser search using your model vehicle and then the terms undercarriage photos. Avoid using diagrams as a term because you will get stick diagrams and no photos.
Some repairs are quite easy, but front seals require separation of the trans from the motor and some tailshaft housings require disassembly of the back of the trans to install rear seals. Depends on whether rear seal is accessible from the end or must be install with the casing removed. Rear seal requires removal of the driveshaft.
Sometimes you can get the photo you need from an individual using a Blog format. Look for Chevy or GMC blog sites, 4x4 sites and so on.

i would check the oil pan gasket, front crank shaft seal, and valve covers. This are common leaks on most gm cars

There is no pressure when the engine is off. You don't have to do anything as far as putting pressure back in other than starting the engine.
Not knowing whats leaking and if its actually the lines then go get a replacement either at the parts house or the dealer.

!!! Why mickey mouse it. ???

Have some one step on brake while you watch for the leak. The fittings for the extention may not be the same as the OE line causing a leak.

Cut that out. Replace it with a compression fitting. Bleed the system.