My car is losing gas and I'm not sure where the leak is

I discovered a loss of 3 1/2 gallons after letting my car sit for two days. I filled up and it didn't leak after a day of off and on driving. I checked under the car and the gas tank looked fine but there was a wet spot on a wide rusty pipe on the drivers side of the tank. Right beside a plastic ring clamp of some sort that was falling off. The rusty pipe has a smaller pipe next to it and a rubber hose of some sort. The plastic ring I think was supposed to be around all three. There is a dried fuel stain on the side of the gas tank near those pipes but no sign of holes or rust on the tank itself. Those pipes are only wet with fuel after driving, and it didn't leak when I had it parked for a few hours in between errands but when I got home tonight it was wet again and I smelled gas. The night I lost the gas I had my car parked on a hill with the car tilted to the left with the drivers side lower. That was the only time I've had to park like that. Tonight I parked it level. I can't Identify which pipe is leaking. I don't want to touch the pipes because rust flakes off when I do. I thought the fuel line was smaller than the wide pipe so I'm not sure if it's a fuel line leak. My mechanic is 30 miles from where I am and I have less than 300 dollars and I can't afford to continue refilling my tank to make more money. I drive in 3 to 5 mile stretches two or three times each day with no long trips. Where do you think the problem is and do you thing I have enough money to fix it, or is it time for car payments again?