The oe filler neck won’t let your syphon hose get to the bottom of the tank. I fought this on mine before I just pulled the tank. To get the tank out be prepared to take the whole rear suspension apart, and the rear half of the exhaust off to get it out. The axle has to droop way way low to get the tank to clear. It sounds a lot worse than it really is. Took me about 1.5 hours just taking my time to get it out. (Way less putting the 4th Gen tank back in) I knew there was fuel in it but with the pump shot I couldn’t get it out. Mine was about 1/4 full and the front leading edge of the seam between the top and bottom halves of the tank was rusted thru from the inside. Once you get a working pump in it you can jump the ALDL connector under the steering column and run the pump. If you pull the rubber supply line off of the fuel rail under the hood you can flush the lines in their entirety with fresh fuel. Make sure and replace the viton orings on both sides of the under hood rubber fuel lines. while I had the tank out I blew air from the engine compartment all the way back to get all the crap out of the supply and return. Make sure and Change the filter. Also if you pull the rubber under hood return line off at the same time as the supply you can run a little air thru the supply and flush the old crap out of the rail before you send it to the injectors. Put a hose or bottle or something similar on the return from the intake or it’ll make a hell of a mess when all that stuff from the rail comes flying out, ask me how I know. The rail and intake lines hold a lot more fuel than I thought they would. The 85-87 cars have better injectors than the later ones. After sitting 20 years I have not had to replace mine. Dont be surprised if your pump looks like this.
Here’s my thread on tgo. Going by my Camaro related forums username of course. It outlines everything pretty detailed I did to get mine running after 20 years.
https://www.thirdgen.org/forums/memb...-new-here.html
I learned a ton about the tpi setup thru this whole thing. If you need anything at all don’t hesitate.