This is how I do it, probably not the only way, but it went ok for me, so please have a look, I hope it will help someone:

The only way that the sealer will stay on the inside walls of the tank, is painting the internal with special tank paint. I buy mine from Mark Huggett, Swiss. P/n for 1 liter is 16 114 080 042 Y (www.bmwbike.com). Excellent paint. The sealer can be applied only after painting.
This method was tested by me with 100% good results. Please take into account that dangerous methods and chemicals are used, also for the environment. That means you are taking full responsibility for your steps bla bla, you make sure that no fire, children, pets and mother in law are around. Use hands, eyes, body and lunge protection. I suggest doing this in the hot summer days, outside in a good vented place and in the shower (!), where water is quickly available. For plugging the fuel taps bores, I made two long screws with matching threads, wrapped with insulating tape. These where screwed to place making sure that the bolt is above the inner surface. If it will not be so, the sealing stuff will sit there and plug the fuel bore… Hot summer day and the use of hot water will help dry the tank between all actions. The tank should first go through "mechanical" repairs, before stepping to the "chemical" repair. That means that all brazing or patching work should take place before inside paint. Outside finish will be done after the sealant.

1.Remove the tank. Drain it. Take off all taps, caps etc.
2.Rinse with Hot water and liquid dishing soap. Rinse well with hot water.
3.Drop inside semi dry tank a handful of sand, small gravel or old nuts/bolts. Shake tank well in all directions, making sure all inside walls gets the grit. Clean inside of tank.
4.Rinse with hot soapy water. Rinse with hot water. Plug tank. Make outside of the tank a caustic soda solution (about 1/2 kg for the tank). Beware! The solution will get very hot due to chemical reaction! Pure into tank (fill it up) and let it rest there for 2-3 hours (and only a few minutes if there are non-ferrous repairs or part in the tank). Drain; be amazed of what comes out. Rinse with hot soapy water (You can unplug it if it helps). Rinse with hot water. Dry tank!
5.Rinse with quality thinner (the ones used for automotive paint are ok). Dry tank.
6.Plug tank. Pure inside tank hydrochloric acid (about 1 gallon). The chemical reaction will eliminate all rust leftovers. Take care! The reaction is dangerous and harmful steam is involved. Make sure all internal surfaces get in touch with it. After 2-3 minutes dry the stuff and rinse with hot water. Work quickly! Dry tank with aid of hot sun and low pressurized air compressor. I use the one that inflate the children's puff-up toys, such as water mattress. Just take one plug out and stick the hose inside. Use a light to be sure the tank is 100% dry inside and raw gray metal is without any rust.
7.Rinse tank with acetone.
8. Dry tank with pressurized air and with sun. Work quickly! You want the paint inside before any rust will build up. Use light to be sure that the inside is dry. Take a look where the sheet metals are joining. All must be dry!
9. Plug both fuel taps bore. Pure special paint inside and make sure it covers all internals. Let the tank rest for 2 minutes on every side of it, including top, taking care it won't spills out. After checking with aid of light that all walls are covered with the paint, it is important to drain extra paint leftover, if there is any. Don't think that thick paint is good! It isn't and will brittle off after a year or so, causing serious damage!
10.Let tank in a vented place for a few days.
11.Assemble sealant stuff according to manual.

I will be glad to answer any question. Good luck!

email (option): michasteinmann@gmail.com

DON'T mix boiling water with caustic soda it will explode and severely burn you

Also, always add the soda to the (COLD) water. DON'T add water to the soda.

Most people already know this, but it's worth mentioning for the few who don't know.

email (option): dannydefazio@sumpmagazine.com

Unless your tank is leaking i don't know why you lads bother with sealing tanks. It's the plastic and fibreglass tanks that seem to suffer. if you do have a leak, use solder.

I used the POV 15 kit from Foster Restorations, which consists of marine clean, metal ready and tank sealer. Seems a bit safer than other chemicals.

Tank still benefits from good prep, I had several sessions rattling gravel in mine to clean out rust, then rinsed and repeated with washing up liquid and hot water.

I plugged the petrol tap holes with cork.

email (option): Adh325@hotmail.com

email (option): Adh325@hotmail.com

That's the stuff. I found it easy to use. Before and after pics below, sorry for poor quality.





First pic is after hours of rattling gravel around and cleaning. The build up of paint material at the end of the tank was to prevent too much settling around the petrol tap outlet. Tried to drain off excess paint but it's very thick.

email (option): Adh325@hotmail.com