#1 Buy formalin (
10% or higher solution). Do not store where it will go below 40 degrees. DO store in a child safe place. It is safer than straight formaldehyde but not safe.
#2 Buy 91% isopropyl alcohol enough to fill the permenant container (you may want twice this much). Read the labels. Most drug stores will have a cheaper and a more expensive bottle the cheaper will be the ~70% solution and the slightly more expensive will be ~90%
#3 Buy/find a clear sealable, air tight container that will house the octopus permenantly. I prefer plastics for the kids.
#4
After you take a photo next to a ruler for final posting on its thread, place octopus in a SEALABLE bag/disposable container and completely cover with formalin. If you use a stronger than 10% solution, you can dilute it with water if you are a little short. Use with caution. Avoid on hand and rinse quickly if there is any splashing (try to avoid and don't inhale much of the stuff). It is very hard to get them to pose so a container (bag) that will accomodate the full length seems to work best but keep the final container in mind before starting. The pose will be frozen within seconds of adding the formalin and they are so limp that it is not easy to set them well.
#5 Seal the container or bag or bag in an air tight container and put out of harms way for a week. At some point (no hurry and a week is likely more time than needed) before you gift the animal, remove it from the formalin (disposal is a bit ecologically sensative, I put it in places in the yard that will not get to the lake and I don't want things to grow but NOT down the sink). Rinse well with buffered salt water to remove as much of the formalin as possible.
#6 Place the rubberized animal (you will be amazed) into the permenant container and fill completely with alcohol. Seal the container. The alcohol is much safer again than the formalin but still not safe so storage and sealing are important. If you failed to remove all the formalin, the fluid in the container may take on a slightly yellow tinge, it can be replaced with new alcohol and resealed at any time.