Thanks for the link wuarhat. I'll be setting up that rig for myself.This is a link to a thread, in a plumbing web site, about the annual flush of tankless water heaters. It's a gas heater, but the flush procedure is the same. You might as well throw the breaker open on an electric model, and be careful not to splash.
Tankless flush - RIDGID Plumbing Forum, Woodworking Forum, Power Tool Forum
Mack.