Wattage for Heating Tape that runs Through An Under Concrete Gutter/Downspout Drain

I live in Montana, so it can be very cold in winter. One of downspouts draining a gutter ends up pouring into a drain in a concrete apron by my back door. The drain goes under concrete for about 30 feet, then another 30 feet of gravel/road mix to appear and drain into a field. I live in the country. A handyman who did occasional jobs for me advised me to get a heating tape, the kind you use for deicing roofs, and put it through the drain to stop it freezing and flooding the concrete patio by...

Wattage for Heating Tape that runs Through An Under Concrete Gutter/Downspout Drain