We have a garden hose flush option in which we do each weekend before we leave. Works good, been doing the same for many years via our last camper.
Called the local dealer (150 miles away) and asked a few questions. He said I wasn't missing any switches and I wasn't crazy. Figured the heaters were 120v and said it should say right on the heating pad. He was as perplexed as I. Said he's never seen this. He mentioned most of the time if it shorts out it doesn't work, not get hot. If I can't fix the tank and need a new one it's a pretty spendy deal with 5 hours of labor and about $300 for the tank. please keep in mind this is in the heart of oil country where the RV dealers are booked and the economy is booming. The service guy was really nice and pretty helpful, kudos to them.
Having it on a seasonal site is really convenient until you need to work on it. I would love to have it at home to do some trouble shooting. Oh well, I'll take some tools with this weekend and some product to see if I can seal it up good. I'll report back with the findings. Feel free to keep posting if anybody has any ideas.