I found a cucumber that got away the other day and upon picking decided that it would make a perfect candidate for saving seed.
To get the seed I simply slice the cuke in half length wise and scoop out the pulp and seeds. I then pull out the large chunks of pulp and give the seeds a rinse.They will still have a lot of pulp around them but no worries as the next step will take care of this for you.Put the seeds in a bowl or container and cover in water. Allow them to sit for three to five days. They will look nasty and gross and may even grow some mold on the top of the water. Again don't worry as this is supposed to happen.