Never had nits. Got crabs once though. The stuff oot the chemists for that nearly burned the bollocks aff me.
Nits are a bugger to get rid of. The conditioner one is the best, and even if the kids get clear of them, still put conditioner in their hair and let it dry, while the nits are still rife in the school. Conditioner stops the wee bastards sticking to the hair so unlikely to get reinfested. Or whale spunk.
washing has no bearing on who gets nits. if anything, nits love clean hair because its easier to climb on.