I use Sunkist Lemons. Find dish washing liquid that mentions "vegetables" under "uses" on the packaging.
Using a nylon scrubbing brush, scrub the lemons for 30 seconds under running water.
Separate the fruit and the skin, and remove the white pith from the lemon rind. Thinly slice the rind into 2-mm thick pieces. Remove the membrane and seeds from the fruit.
The jam will be very bitter if you don't remove the white pith.
Place a small amount of the white membrane and pith in an empty tea bag. Set aside for later use to extract the pectin.
Put a pinch of salt in boiling water, then boil the lemon rind for 15 minutes, drain, then add fresh water. Repeat this step 2 times, soak the rinds for about 3 hours in water, then drain to remove excess water.
Place the drained lemon rind and fruit (with the juices) in a sauce pan with the tea bag filled with the white membrane and pith. Add sugar, stir, then simmer on low heat.
After 15 minutes, remove the tea bag. Skim off the scum that rises to the top.
Simmer for 30-40 minutes on low heat after adding the sugar. It's done when it starts to slightly thicken. It will thicken more once it cools.