I'm on the 'don't drain'
side of the cooler equation, so I wasn't concernced with keeping the drain hole clear. However, as Coloradopaddler suggested the ice melts at the edges first, so I could have drained as needed.
I only drain to prevent water from sloshing or when the ice is finished. On a 7 day trip I might open the drain a bit on day 4 to get the water level below the ice level, then drain completly at day 7 when the ice is gone.
I'm am an admitted cooler nazi. No one goes into my coler except me, and I don't go into the cooler unless I absolutely have to. Even then I try to minimize the open time and coordinate my access for late in the evening or early mornings. If I'm not cooking that day the cooler stays shut, period.
I also made an insulating jacket for the cooler out of bubble wrap style insulation and duct tape. I figure the reflective surface helps fight the sun and adds about 50% more insulation. Plus the hassle of removing the jacket reduces casual cooler use.
bubble wrap insulation
24 in. x 25 ft. Staple Tab Insulation-ST24025 at The Home Depot