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This may seem a bit of a silly question but is there a preferred way of draining the fuel tank without removing it. I have an old TR7 where I think the fuel has well and truly gone off. Any help gratefully received.

Thanks

The following assumes the car is not a fuel injection car because the process may well be different as the fuel tank is kept under pressure.

Stick the rear wheels up on ramps and stick some bricks under them just to be absolutely sure the car cannot collapse on you. Crawl underneath and remove the petrol sender unit which leaves you with a small diameter circular hole through which you can stick a syphon unit (these cost a couple of pounds from most motor factors). Pump out all the fuel and use a mirror to ensure you have got right into the front of the petrol tank and sucked it all completely dry. If possible, check the front, lower section of the tank is not corroded as this is where they all fail because it's where water collects.

If the retaining plate for the petrol sender unit is buckled then get onto Robsport or S&S and a new one will be with you the following day. Mine was buckled last time I went to remove it nine years ago. And yes, the front, lower section of the tank was corroded excessively and the cause of all the misfiring necessitating a new petrol tank. Not the first time it had been changed either hence why I now have extra weather protection over the petrol cap. Best of luck.

Thanks for that John.

John_C wrote: ... remove the petrol sender unit which leaves you with a small diameter circular hole through which you can stick a syphon unit ...

Before removing the sender unit make sure that the fuel level is low enough otherwise fuel will be all over the place.
So first remove the filler cap and disconnect the fuel line between tank and steel pipe.
Disconnect it at the car's side and stick the end in a suitably large container, and leave it there till there's no more fuel coming out.
This way (though more time consuming) will almost completely drain the tank.
After that remove the sender unit and remove the remaining fuel with a syphon unit and/or paper workshop towels.

If you just want to drain most [almost all] of the fuel, just remove the hose from the fuel pump, & weigh it down as low as possible. This will syphon almost all the fuel out, without mucking with the sender unit.

When trying to clean the rust residue from the tank, through the sender hole, I jack one side of the of the car up about 2 inches higher than the other, then suck from the front low corner of the tank, as you can get more of the last bit this way. If trying to get fine silt, return clean fuel, strained if necessary to the tank & re-syphon a couple of times, as you will get more each time.

To stop any condensation or other water that gets into the tank from causing rust, add some Morey's upper cylinder lubricant to your tank. This stuff may or may not help your valve gear, but it is preferentially absorbed by water. It makes the water oily, & will leave a mildly oily surface on any part of the tank the oily water touches, preventing rust. I doubt it could save a 25 year old well rusted tank, but should extend it's life, & extend indefinitely the life of any new tank installed.

Hasbeen

I drop 1/2 litre of isopropyl alcohol in the tank when I park up for the winter. I read that this absorbs condensation and then burns with the fuel. This is ever since I had a bad start to the season when it started pulling through a lot of water and muck and obviously running very rough. I emptied the tank, basically using Hasbeens method plus a pipe down the fill pipe and drill driven pump. It still clogged 3 inline filters when filled with clean fuel before it ran clean. Not had a problem since adding IPA.

A couple things to bear in mind:
FI fuel tanks aren't under pressure but under a slight vacuum as are N/A carb machines (to keep gas vapours from entering atmosphere).

If you are going to drain all the old gas you might as well open it up and view through the hole to check condition of the tank. Just like not going to the doctor so he can't tell you something is wrong isn't going to keep you healthy, not knowing the condition of the interior of the tank isn't going to keep it from rusting. If it is rusting, time to drop it, remove rust, condition the tank with zinc and seal it so it can't rust. This is especially important if you have a two hole FI tank as they aren't available and custom tanks are expensive. Waiting until your tank rusts out and having to keep changing gas filters is like taking cough syrup to take care of pneumonia.

Sorry for the slow reply - Thanks for all the advice, will probably take the easy option and go from there. The car is not road worthy at the moment so I am just pottering with it trying to get it mobile