Plastic fuel tank is made from HDPE plastic ( High-density polyethylene)
Most PE plastic grades have excellent chemical resistance, meaning they
are not attacked by strong acids or strong bases, and are resistant to
gentle oxidants and reducing agents.

That is why PE plastic is very hart to “fix” by glues. You can use special
kind of 2 component epoxy glue. Epoxy glue is rigid not elastic. Plastic fuel
tank contracts when cold and expands when hot epoxy glue cracks and
you have a fuel leak again.

I will show you how to fix PE plastic by heat. With solder station heat
problematic area fill it with small piece of PE plastic and you are done.
In this way crack is filled with the same kind of plastic that behaves
the same as original. When fuel tank contracts and expands treated
area will do the same.

Step 1: Find HDPE Plastic

Find peace of HDPE plastic you can use to fix the crack. I have found the best
place for that is empty detergent bottles. Detergents are chemically aggressive
and the best way to store them is in HDPE plastic bottles. Perfect for your
mission. On the bottom side look and find markings like on pictures.

When you find HDPE plastic bottle cut out peace 1 cm wide and 10 -15 cm long.
Create a small plastic stick. Wash and clean the plastic stick with water.
Dry with paper towel.

Step 2: Prepare Problematic Area

Empty tank from fuel. Leave tank opened. In that way fuel will not make
pressure inside tank. Use sanding paper and sand around problematic area.
You can use medium rough sand paper. Sanding is necessary because of 2 things.
First you will clean area and allow PE plastic stick to better bond with PE tank.
Second, sanding debriefs will fill crack inside. When you apply heat it will help
in filling the crack better

Step 3: Fix the Leak

Take solder iron. Set to temperature between 250-300 Celsius. It is better
to use wider solder tip around 1cm wide. It will help in dissipating the heat
evenly around crack. If more surrounding area is heated plastic PE stick
will bond better to PE tank. Take plastic stick in one hand and solder iron
in another. Apply heat to tank. Remove solder iron place stick on tank
and apply heat on stick. You will feel that peace of stick melts and bonds
to tank. Then move 1cm along crack and do the same.When you are done
in melting the stick along the crack take sand paper again and sand the place.
If some of the PE stick is not properly melted and bonded to tank it will fell off.
In that way you know which place of crack you have to do again. That’s it.
Crack fixed and you can fill it with fuel. It took me around 20 min to do the job.