Open the front hood and you can smell the gas, and I can tell it's coming from the underside of the tank (new gasket on the topside).

I also had this problem last year. That's when I decided pull and refinish the tank (inside and out). At that time I replaced the tank filter sock and all washers, the fuel filter and all of the soft lines under the tank. Fuel smell gone! At least until this week when the smell of fuel returned with a vengence. Enough to stink up the garage when I open the hood.

The rant is that I hate pulling the tank. It's a royal pain. So far it's been one of my least favorite jobs. Also, I hate that all of the work I did to get rid of any gas leaks/weeping lines etc, only lasted for a year. I also hate that the 'access' hole on the underside of the car is barely accessible by anyone- except for maybe rats and spiders.

Ok, rant over. Back to your regularly scheduled day.

Sounds like the threaded nipple on the bottom of the tank is loose!

I had this problem and I was able to put a claw type socket on my extension and tighten it from the bottom!

I feel your pain. All the guys here say "run the good german hose". I say nay myself. The west coast fuel just ate the crap out of it. I use the high pressure FI hose for as much as I can. Expensive yes, but the stuff holds up.
Just my 2 cents.

BTW for the "old" metric argument...

5/16 hose is .3125"
8mm hose is .315"

.0025" is less than the width of most human hair. About as much as a single sheet of paper. It makes no difference.

7 mm can use 1/4 but its .025 different. Thats tougher to use. (1/4 being smaller).

The 'good German stuff' I replaced last year with high pressure FI hose. Hopefully I just need to tighten the fittings on the tank as Jeff suggested. I really don't want to have to pull the tank again. Do folks use anything on the threads like plumbers tape or something?

It's a '75, so at least I can take a look at the fuel pump & filter connections fairly easily.

there is a "fiber" washer that must exist to provide a good seal on one or both of the fittings ..?

I had new fiber washers, too. I haven't had a chance to get under the car yet, but hopefully this weekend I'll get a chance to see what's causing the problem.

Then don't use the access hole.

Instead of a 6 or 8 inch hose and having to go under the car to connect/disconnect, make the hoses 3 ft long. The extra hose won't make a difference on fuel delivery and will allow you to be able to lift the tank completely out of the cavity without disconnecting the hoses.

The hoses should go from the tank, then loop over towards the driver side then back to the tunnel tubes.

To hold the tank up while making/breaking connections, I use a couple of 2x4s between the bulkhead and the cowl. You can even start the car with the tank out of its cavity. I traced a fuel pump leak doing this.

I did make the hose much longer than the original 6- 8". Good idea regarding the 2x4s to hold the tank up. I hadn't thought of that! Hopefully I gave myself enough room to have it up that high and still connected. My guess is that i wasn't thinking that far ahead at the time.