I wash my overpants everyday.
With rubber pants, which I wear over pin-on birdseye prefolds, I wash them by hand in the shower with bar soap and warm water after every wetting (I wet very heavily, soaking my diapers to leaking), or wetting and soiling (soiling permanently stains the rubber, but that's the price one pays), and I wash them once a week or so in the washing machine with diapers only (no pins, no zippers, no buttons -- nothing that could puncture or scar the rubber).
I never, ever dry them except by hand, wiping them with a hand towel inside and out and placing them on the radiator for a time so them may dry without drying out. The waistband takes a long time to dry, but it's worth the wait. If one does not wash these pants with baby detergent now and then, they will retain not only pee but poop smells, which can be very unpleasant over time. Properly cared for, these pants provide remarkably warm, soft, comfortable, effective, and sanitary protection.
I also have wonderful Gary high-backed Euroflex pants, which are transparent. Very soft and pliable yet truly durable and protective. These take well to the same treatment as the rubber pants -- washing by hand in the shower after wettings or soilings (they don't get stained as do real rubber pants), followed by hand-drying and gentle radiator-time. I do wash them occasionally in the washing machine, but I never, ever dry them except by hand. They tend to develop pee odor if not washed with baby detergent in the wash once a week or so.
With my Netti PUL SuperSoft pants, I just put them right in the diaper pail with the wet or wet 'n' messy pull-on cloth diapers and wash them accordingly. The beauty of PUL pants (polyurethane laminate, with polyester) is that they breathe, allowing urine and sweat to transpire without too much leakage. (They will leak through if a diaper is flooded.) This helps to prevent the funky curdled-pee stench that can permeate vinyl or classic plastic pants.
I gather (no pun intended) the new PEVA textile, which I haven't yet tried, works well at preventing unwanted residual pee odor (I do like it too, but not if it is too skunky or ammonia-laden, and I do love clean pants) and enables the pants to be washed and dried more often and at higher temperatures without the pants' drying and cracking. Netti PUL SuperSoft pants are great because they stand up to hundreds of high-temp washings and dryings; they are made for industrial settings, as are the Gary pull-on cloth diapers -- pretty much a daily daytime combination for me.
Finally, my Salk SaniPants (a classic babyish snap-on textured poly pant with cotton leggings and a wonderful old-style waterproof liner) really require regular washing in the machine to keep them clean. They don't stain too badly (a blessing), but they develop strong odor readily, as they are surprisingly retentive yet just do not breathe very well. Overdrying will lead to cracking of the waterproof liner (reminiscent of days of multilayered baby pants from days of old), but they must spend some time with their brethren in the dryer combine, lest they never dry out and become not only redolent of pee but musty and mildewed. Yuckinesses to be avoided.
Happy nappies and snappy pants to all.