how to disinfect washing machine

hi friends, i am using my washing machine for washing my inlaws cloths which are mostly urinated.iam not finding fault with them.its due to aging problem.the problem is i am washing every one s dress in that washing machine only.(but seperately)i ll make a long gap between washing their cloths and ours.i ll wait for the machine to dry completely.then start the other wash.is this ok? or how to disinfect the washing machine?if using dettol or some thing hw much i can pour in?:idontgetit:

 

thank u sbmat and sonal for ur suggestions.