These are both simple (use impact wrench on anode) compared to descaling.    

It's compounding interest v simple interest and making $ work in two places at once.

Mail out flyers is the best way.You can drive around the area that you are interested and see if it looks abandoned and find the owner.It's off-market so it means a lot of manual work on finding them. do a simple internet search and you will find many ways.

Also, if I had no desire to at least take time to  see it, Id make life simple and invest in a CD or high yield fund. 

This approach reveals more about the tenant’s behavior and reliability beyond simple yes or no answers.Check multiple referencesContact at least two previous landlords for a comprehensive view of the tenant’s rental history.

I’m simple and would be fine with just 10k/month with fewer properties.

You can usually find some events by doing a simple google search.

How would I do that - send them a formal invoice or request, or can it be less formal like a simple email? 

Just RUBS it yourself, using a relatively simple RUBS spreadsheet and open & transparent billing to your (new) Tenants.

I would also consider "private money" from friends and family for your first deal as well - maybe offer 8-10% simple interest and see if anyone would be interested.