If you reprogrammed the siphon, one of the thinner curtains will come down. As you go through the tunnel, and find another curtain of thinner, there will be gears to turn, that will lower the next curtain.
At first the gears will be in the tunnel, then, the next three areas will have the gears in tunnels just off the main tunnel -- you will be able to see them through the bars.
Don't get turned around. Look at the paint containers that are above the gears, levers before spinning and pulling. Keep track of which side of the tunnel the sub-tunnel was on.
THE WAY TO REPROGRAM THE SIPHON is to have Mickey put an ANVIL on the round pressure plate. Then, Oswald will zap the power box on the central siphon (while you stand in a little saver place, a few feet away, like behind a car or ledge). If Oswald does not get there in time, you may have to drop another.
In the beginning, I just stood on the pressure plate. I would thin a tree, and eat the red fruit, to get my health up, stand on the plate, and eat some more fruit.
When I came to the tanker shooting at me, I jumped on a car and a tree, and dropped a watch, at TV for him to watch and hold still, and then hit him with an anvil. For the floating dropwings, dropped a watch sketch, then I befreinded them.
EDIT: Gas cans and bushes have health, too, if you spin them.
I do not deal with the cars. If you destroy one, it will respawn, and there are too many in too many different areas. So, I just drop a watch sketch and out run them.
In the area where there are two pressure plates, and the cars are on the ramp, I paint the ledge on the far side, and go down there, away from them.
After the siphon is taken care of, I sneak where they cannot "see" me, and then I drop a watch and run through the tunnel.
(Cars cannot go into the three sub-tunnels, where the other gears are.)