The washer in this house is a fancy Samsung HE (high efficiency) washer that cannot be used to wash things that are waterproof, such as diaper covers. So I found a glass washboard at an antique store, for $14--about half the price that I have ever seen one for sale--and have been using that to wash diaper covers by hand. The washboard is a big help for the covers that need scrubbing. (Glass washboards were preferred over metal ones in the old days, though I forget why.) With the washboard, it takes me about ten minutes twice a week to wash my toddler's diaper covers.
With a new baby, I will be washing diapers three times a week instead of two, and will have a much harder time finding ten or fifteen minutes for handwashing covers each time. So I have been preparing to switch back to wool covers, at least during the daytime, and to machine wash them (see below).
For wool, I had a small amount of wool yarn leftovers, and four old, stained, and shrunk cashmere sweaters that my mother-in-law passed on to one of our children. This child made an honest attempt to appreciate the qualities of cashmere, but fundamentally just isn't a sweater person. Only one of the sweaters was in good enough condition to donate, but they were all too good to throw away.
For diaper cover patterns, I looked at the plastic-pants-style covers that we had, and measured them, then drew up paper patterns.
I used the yarns, in a double strand because they were sock weight, to crochet most of one diaper cover.
Then I cut as many cover pieces as possible from the sweaters, and then stitched the larger scraps together patchwork-style, and made more pieces from those. I put elastic around all the waist and leg openings, which cost about $5. All together, the four smallish sweaters plus the crocheted yarn piece yielded four large covers, six medium, and five small. The cashmere is soft and beautiful. With the wool covers that I have from before, which will be usable with the addition of a little elastic, this gives me enough to use wool covers full time, if need be.
For water repellency, wool covers do much better if they contain some lanolin; lanolizing instructions here. Also, generally handwashing (and only occasionally or when poopy) in lukewarm water with air drying is strongly recommended for wool covers, to prevent them from felting and shrinking. But what I have actually done in the past is to skip the lanolin, wash the poopy wool covers in both cold and hot water right along with the diapers, and hang them to dry with the other diaper covers. Most of them felted and shrank (some wool won't, even if you try), but that gave a nicer density to the cover material, and only some of them ended up too small. This batch of diaper covers runs large and roomy, and most of the material has already been shrunk, so I'm not worried about shrinking. But I may start handwashing them once the baby gets into the medium size, just to keep the cashmere from wearing out too quickly. My babies don't stay in the small size for very long.