Then if the market tanks, buy even more.

But we just replaced a HW tank on a SFH that we rehabbed & my partner 7 years ago decided it would last a few more years.

Add in the underground oil tank and what looked like a $40-50k rehab probably would have been significantly more.There is a learning curve to walking a house and knowing costs to rehab, but it's all part of the game.

The lots have septic tanks installed already. 

I am also considering going tankless because I have the wiring to do it.The old water heater tank failed so I am serious and ready.  

I am creating our lease for our property that has a septic tank. 

If you have lots of sludge in the tank that blocks the outflow, that probably means the tank doesn't have a lot of cultures which eat at the sludge layer, so it introduces them and they do their job, which eventually unblocks the outfow. 

Compare that to buying a stake in Tesla, and Elon decides to tweet about "420" and tanks his stock, or any other corporation that can have accounting fits any given year and your get massive stock movements.  

We just discovered that we have no septic tank and our sewage is running out on the neighbors property.

If he doesn't, his BBB rating tanks.