I've been using this for cloth diapers for a while and it's really simple.
1c flake or bar soap (felsnaptha is easily found at grocery stores, but any bar will do)
1/2c borax
1/2c washing or baking soda
If you use bar soap you need to grate it; or let shavings soak until they dissolve. To mix ahead grate soap as small as you can get them if in bar
form. Mix soap flakes/grating with borax and washing soda. Use 1/4-1/2c in a large load, one or 2tbsp in a small load or front loading machine. Rinses
really easy. Can also be used as a general purpose cleaner for things like counters, floors, tub, toilet, etc. Putting vinegar in the rinse helps
cloths feel soft and helps eliminate odors. If you need to wash by hand, you can just scrub the cloths with the bar soap, put a tbsp of the washing
soda/borax mix in the wash water.
In a pinch you don't need the soap, but your cloths won't get as clean as western society is accustomed to. I don't think it will be a major
concern in a sitx.