DIY Laundry detergent(yes, it's a detergent for most water types, not just a soap). Works better, costs less. Here is how I do it.
#1 Bar Laundry soap(Fels Naptha)
I buy a bulk package of laundry bar soaps. You can get a 24 pack of Fels Naptha for like $38 or just a single bar for $2. I do this to save money and time, so I just do a huge volume of it at once, therefore the $38 is more up front than anything.
#2 Lye
I make my own lye-base, mainly because I run a dehumidifier and use a wood BBQ(search the web on the process, but it's basically a set and forget until you need it kind of thing). But you can buy enough lye for $5.
#3 Borax
One box will make the sized batch that I work with. $5
#4 Baking Soda
One full box. $1-2(when baking soda is on sale, I buy 4x because it's frikking baking soda and has too many uses). But for the DIY detergent, one box is all I use.
Process the fels-naptha bar soap. I put it all into a bucket. I use a drill with a funny attachment that I made for mass-grating potatoes. It's basically a hole-saw with a few holes that I drilled into it and punched out to give it a rough edge. It takes about 10-15 minutes to get all 24 bars ground down, then I take the final big bits, break them up by hand and just throw them into a blender. You'll have a powder-like consistency if you do it right.
Then I boil about 3 gallons of water. I use two 5-gallon buckets for this so I can split the work in half. pour and mix the fels-naptha and water evenly. It will melt, but still have chunks. The good thing is, if you keep the water hot, the chunks dissolve on their own. I see some people constantly mixing their DIY soap, and I think that's mainly because they leave their burner on. Either/or works fine, just don't burn the soap because it will stink. Then mix the baking soda and borax equally within the batch.
The lye will dissolve fairly easily, so I add it AFTER to prevent heat loss from melting the powder. But I guess it doesn't really matter if you add it before or after, just adding later saves some elbow grease. I only add about 1 cup of lye for the entire solution.
Once it is mixed to a butter consistency, let it sit for a few hours until everything separates. I've done this overnight, works fine. Then you do a final whipping and you're done.
2 TEASPOONS of this will wash a standard load. It's fine in HE washers(just don't use it in the dispenser, put it directly on clothes). Dirty loads, big loads, maybe a tablespoon(3teaspoons) Do not add any oils or fragrances, as it will actually ruin the batch. It smells good and clean as is, works as good/better than Tide, Purex, Surf, or any other store bought detergent. But you can use whatever fabric softener that you want for smell(using the timed dispenser), although this DIY detergent WILL not only clean clothes, but also soften them(another money saver).
The bottom line?
The batch I make costs around $60 in supplies.
Cost per load: Less than $0.03 and this batch will last a few years. Compare that to $0.50-0.70 per load of the store bought brands.
-You can make a small batch for as little as $12(without lye, and still have leftover supplies) to try and see. That winds up being around $0.10 per load.
You also can use other laundry soap bars. But naphtha works best for me. Tide makes their own bar laundry soap, zote is another one. I think some non-naphtha bars might be a must for anyone who wants to do this, but finds their skin easily irritated by different laundry detergents. I have sensitive skin, and I have never had an issue with this detergent. YMMV
