Water overflow?

Kenmore 90 Series washing machine

My washer has overflowed 4 times in the last 18 months. My appliance repairman tells me that it has to do with lint/soap clogging up a valve, and showed me how to remedy it by blowing into the tube. This strikes me as a solution that I can only use after the fact. What can I do to stop the problem from occurring in the first place? Any help is most welcome.