Suitable answer from her to him, "Well, if is not such a big operation as yours, perhaps I will have recovered from it in (fill in X weeks) and you will only have to look after me for that long, instead of the (fill in Y weeks) that I have been looking after you. Bear in mind that if I get an infection in it from emptying the cat litter tray before it is properly healed, you will be waiting on me hand and foot for (fill in Z weeks)"
Perhaps she should leave the litter tray beside his plate at mealtimes until he decides that he does do emptying it.