We don't insist on Small helping with housework, but we do explain that it is helpful when we all work together to keep our house nice to live in.
Sometimes I will ask if Small can help me with something and he will refuse, in which case I try not to force the issue.
Sometimes he is very helpful - in the last few days he helped me cook dinner, laid the table, took his dishes into the kitchen, helped me clean the bathroom, helped me put away clean laundry and put dirty laundry into baskets.
He may not do any housework for a week now, but that's OK. When he does help, he does it because he wants to and not because I have forced him.