My parents have a grapefruit tree and a lemon tree. I get lots of lemons and grapefruit. Over the years I have investigated innumerable ways of using and preserving this bounty. I can lemon juice for year-round use. I eat and give away as much grapefruit as possible, then can the rest. This leaves me with a mountain of grapefruit peels. It seems a waste to throw them out, and they don't compost well. So one year I started experimenting with using them to make a cleaner. It didn't take long to hit on a simple formula that is also very simple to prepare.
I get out my biggest stockpot, fill it with grapefruit peels, and cover them with water. I bring the whole shootin' match to a vigorous boil, then turn it down and let it simmer for a day, topping up the water level as needed. After several hours, or all day, I turn off the heat and let the mixture cool off overnight. The next morning, I get up and start straining the mixture into gallon size glass jugs. Do not use plastic, as this concentrate, though not really rough on the skin, will eat through plastic jugs within a few days and leave you with a leaky mess. It is also a good idea to vacuum seal or water bath can (in quart-size jars) any concentrate you will not be using right away, as it will ferment and grow yeast. This fermentation does not make the cleaner lose any effectiveness, it just replaces the pleasant, citrusy scent with an unpleasant odor.
Be sure to label the concentrate so no one drinks it. I don't know how harmful it would be, but I certainly don't recommend it.
A note on straining. I put a funnel on top of the glass jug I am straining into and line it with a piece of old t-shirt, sheet or dishtowel to filter out the solids. The liquid is too thick for coffee filters, it takes forever, and does not need to be strained as much as that. I then ladle the liquid into the filter, scraping solids off as they build up. When I get down to where it's mostly peels and other solids, I squeeze them real good, filter the remaining liquid, and put the now softened peels into the compost bin, where they compost much more readily.
How to use your fantastical new cleaner. For general cleaning, I dilute 1 part cleaner to 4 parts water in a plastic spray bottle. At this dilution it has not eaten through any of my bottles yet. This works well for light cleaning of counters, glass, mirrors, sinks, toilets, floors and all such general light jobs. For laundry, I use 1/2 to 1 cup undiluted, pour in with the soap instead of bleach, and enjoy softer, whiter, more pleasant smelling clothes. For tough, greasy jobs, like my stovetop, I pour the undiluted concentrate right on the greasy spots, let soak at least 20 minutes, then use a hard plastic scraper to loosen most of the cooked on grease. This does sometimes leave a few small areas to scrub with steel wool or a copper scrubber, but takes most of the work out of it.
I have used this same formula with orange peels, lemon peels and combinations of different citrus peels, in smaller and larger batches. The basic idea is just cover with water, cook several hours, strain and enjoy using your own homemade, all natural citrus cleaner.