I wash my kit after most trips. furry suit and under layers get a rinse in a bucket if likely to be muddy then go through a rinse cycle in the washing machine then every two or three trip through a wash cycle with other laundry. The oversuit gets a thorough sloshing in a large bucket/trug a number of times and then putting in the spin dryer.
An old previous washing machine I had, I wasn't so careful about slightly muddy kit going through, but in time, despite cleaning the drum, I found I was occasionally getting muddy (definitely from mud) skid marks on other clothes. Eventually I stripped the drum out to find that years of congealed soap powder on the inside of the outer drum that were brown with mud that would occasionally make a bid for freedom. Bits of this muddy paste would find themselves inside the inner drum and pressed into the washing when on a spin cycle. So despite the machine appearing to be clean and mud free, there was quite a bit of mud infested soap powder trapped between the inner and outer drums.
Back to the oversuit cleaning - After sloshing the oversuit in the bucket of water the first rinse water is throw on the garden, any further rinsing water goes into a dustbin for the mud to settle out and then gets reused next time. The result is only one bucket of clean fresh water used as a final rinse. Whole process takes about 15mins.
A few reasons for washing kit after every trip:-
Much nicer to put clean kit on.
No shedding of dust from oversuit and leaving and dust cloud to settle in the next cave, particularly important in the well decorated caves of Mendip.
Helps keep the dust down in the car and house between trips.
If I find time I can then carry out any repairs to oversuit.
Digging twice a week means an extremely muddy oversuit.