POR 15 coating I will use minimal acid, and essentially not blow holes in any but the most marginal of tanks, and get it all treated and coated. $60 and return shipping. Make sure you send it in a good box, its comming back in the same box with pretty much the same packing.
Turn around times are prolly going to be over a week, and will get longer in winter cos its totally dependent on the weather as well as take a good 3 days to have the fumes dry out and the coating cure on warm days.
I also will try my best to have the coating not get outside on the paint, but no guarantees here, the fuel fitting and vent will have to be cleared as a priority so I'd make sure of that before preserving the paint.
Yea, send it with the fuel fitting in it.

Added 09/27/08
I can also undent the tanks in effect taking out all but the lightest of ripples. $50 for a 1 panel undent. More if you have 2-3 far apart areas. Because each hole needs to be cut right where I can get at the dent with a number of large fist sized + devices and hammers and rollers.
This is done the old fashioned way - by hacking a palm sized hole on the under side of the tank and hammering out the dent, rolling it with various home made metal and plastic and rubber devices etc etc etc ... Pics of a recent one here.
http://picasaweb.google.com/srinath.the.man/TankDeDenting#

The tank ideally needs to be coated after this, I wont count on the weld to seal up 100% and the weld will rust and rot out very very rapidly unless protected by paint and coating. $10 discount if coating and undenting is ordered at the same time. I will help the acid step by sanding up the inside well, then get coating done with a lot less acid and chemicals. I would brush coat POR 15 which is usually far superior to the gravity and rolling method. After welding, I'll coat that weld area with brush as well. Run a pressure test and send it off. I am still working on the pressure testing part - the yellow one for smithville flats may be the first of the ones with a pressure test. Yea I will spray the outside of the weld with some paint so it dont rot away from the outside.
Cool.
Buddha.

This is a nice price. I called 5 radiator repair shops in my area to ask about Redkote lining my tank (not POR15). 3 had no idea what I was talking about. One didn't do it anymore (too many complaints about coating peeling) and the last one charges $195. F it. $20 of phosporic acid nitrile gloves from Home Dept, $1 of baking soda, and $50 of bedliner (instead of paint)  from Walmart will do fine til next spring...

What the ... bedliner ... maaaaaa ... how well does it hold up ... and if it has to come out ... how will it ever come out.
Its pretty much the same math for me ... but like add $10 of POR 15 and 3 days of rolling the tank around from side to side ...
This will not ever peel, there is some on my driveway that is not moved in a year. The thing will outlive the bike and heck, the coating will be holding in the gas as the gas tank rusts from the putside and crumbles ...
Cool.
Buddha.

BTW being 1 man with no real overhead = huge advantage. Spare time ... I prefer to sell my brains and a little bit of the dexterity I seem to have obtained ... like digging out tiny ass bits off carbs and go ... ah-ha, this is bad ... when people go ... you can see that ...

And yea - whoever thought that huge lumbering corporations are very very very inefficient.  ...
Cool.
Buddha.

Bedliner for the outside. One guy pays more for materials, but less for EPA fines

What ... EPA, bedliner ... dang it that's some strong hooch you got there
Cool.
Buddha.

what do you do with the POR15 after you use it?

The general idea is to drain it and let it dry up and waste it ... that is the POR 15 clown's favorite thing to suggest to you. That and  "strip it out and start over" ... no matter what your question is.
I have however developed a formula ... where I do 3 GS sized tanks or 4 smaller tanks at the same time. I dont have left over (or have very little). This time I also has 2 GS tanks of my own and a square box like tank for someone's bio diesel project. The excess got dumped in that, I sloshed it and it was just about right for all the POR 15 I bought. They give you about 1 pint in a kit, and I dont think that is too much, and its not too little for a GS sized tank. So it may not give you much excess.
Cool.
Buddha.

Ok, so if I send you the tank, what do you recomend flushing it out with first to get rid of the residual fuel? 

THanks.

I'll do that, just send it as drained off fuel as you can.
But very hot water will essentially displace and evaporate gas, 2-3 rinses with that and it should be devoid of gas. As will water with simple green etc etc.
Cool.
Buddha.

How long from new can you expect to get out of a GS tank before needing treatment.

Is there additive treatments you can buy to add with fuel to give a longer life?

Should I start looking at placing in line fuel filter (bike is new 400km on clock)

Just curious, thanks
Steve

Ha ha ... I have seen the insides of my 86 yamaga maxim 700, its has a rough life with atleast 5 years of sitting in the weather un used ... and its tank clean and shiny inside. Rust outside, especially where I dropped it and dented it and scratched the paint etc etc, inside, shiny.
A non rusted tank, I'd just try to keep it full. The rust coating is designed to stick to a rough and pitted but non rusted tank. Maybe just protect it. Keep it full.
Cool.
Buddha.

Look up Gas Tank Electrolysis.  There is a video of cleaning parts with A&H Washing Soda, water and a battery charger. The great thing about it is you cant over do it. It will only remove rust, not metal.

This is Otis's buddy. 

I ahve heard of that electrical methos back on 2001 or even earlier. I am worried about its properly cleaning the crap pockets etc. Electricity is line of sight almost. Acid on the other hand attacks the nooks and crannies better, cos the acid gets caught in there and like de rusts it better.
Anyway I'll experiment on my own tank with the electrolysis.
I am adding a new twist to this. The flat $60 is only for GS tanks. I did a shadow 600 tank for someone and other tanks like my nighthawk etc are much much harder for their various designs. GS is just about the easiest IMHO.
Cool.
Buddha.

got a tank that was badly rusted. used the "tank cleaner" multi step process that i bought from a local shop. really  not confident it went well...guy working on my carbs suggested a new tank.
any way to tell your process will do the job? with tanks over $500...thought it worth a shot.
thanks.

Oh crap, I dont believe I replied to you.
Anyway, It will work just fine as long as your tank doesn't have a lot of holes in it. I'd know when I toss in the acid BTW, the method I use I have brought so many tanks back from the brink.
The one part where it can fail is if it had a gash, and you patched it with gas tank patching type thing ... it can come loose a few days to months after.
But yea send it and I'll do a honest assesment before getting into it. Pics etc etc will also be sent to you via email.
Cool.
Buddha.

I am actually going to drill a hole in the top of the tank, put in a vent tube and you can run a hose out of it with those 1 way vent valves like on the 80's sport bikes (which GS is) ... if the tank will be painted anyway. If not ... figure a bit of lumpy looking coating. I like putting a lot of coating stuff in it, sloshing it and sitting it with it on 1 end, then draining it. It makes for the right thickness, smooth as glass coating with all the dust and crap out of it when it drains. It also helps dry the tank, and to drain the acid etc etc etc.
If not painting it, I may have to drill on the underside  ... just where the mount bar goes and weld a threaded boss and bolt it shut when done.
Cool.
Buddha.

 Hey  this  may  be  a  stupid  ? .... I  don't   know    Maybe.....  I  have   a  tank    with   exsiting  rust........  one  hole  rusted  through . can you  do  anything  with   this  tank?

Rusted though must be welded shut. Now if its very thin around that rust, its prolly a goner.
Sorry I didn't see this post, you should PM me.
Cool.
Buddha.

Hey Buddha - I'm pulling my bike apart after a crash and noticed some rust in my tank. I'd like to get it taken care of, but have a quick question first. I don't understand if you actually drill any holes in the tank when you clean out the rust. I have what looks like very minor rust, although there is quite a bit of it. No worries about hurting the outside of the tank, as I've been in the process of repairing it with bondo (got a pretty good dent in it) and any paint that comes off in the process of the coating would only help me in the long run. So how does this work for minor rust? Do you need to cut/drill any additional holes in my tank? Thanks in advance.