Remind him to clean out the filter. Maybe once he does that he'll understand the mechanics of the cleaning process and 'cotton onto' the fact that the dishwasher isn't magic. If it's not used properly it will fail. Guys are practical creatures, very visual. I suspect that he will need to see with his own eyes that if the large scraps of food aren't scraped off the plates that they WILL accumulate and gunk up the machine in the filter and pipes... and then he'll have to fork out for the cost of a plumber to ungunk everything. Also the idea of re-circulated gunky water from months of accumulated old scraps of food might not be a very appealing idea ewwwww!