After the 90 day flip rule came into effect, I now compete with the average local investor for the most part.One large downside is that if we finish rehabbing a property in a month, is that the property is now vacant for the next two months unless I can find a conventional buyer.

Now how that all actually plays out with insurance, attorneys and courts in individual cases, and at what costs in money and time, that's the rub.There is usually an insurance policy on the tank, to cover leaks, as part of the price of the fuel, so check with the seller on that.I would certainly recommend making your deal contingent on a clean leak test (and decommissioning if that's what you choose) and have your deal effectively read such that if the test comes back with water in the tank, ie the tank has leaked, then you can walk from the deal and get your EM back.The existence of a UST, especially if in use and not leaking, in no way needs to be a required deal killer though. 

Or,would it be effective to send it to the deceased address hoping that it would get to person in charge?

In order for there to be conflict you are insinuating there is a negative effect to the Association or other owners from the board members actions.

The side effect of that is they will repossess from time to time and own property.Again, I'm not up to speed on all the ins and outs, but I do seem to recall there are time limits for certain things.  

Would door knocking be effective?

Some folks I know find them effective; others, not so much.

This is not to blame that the tenant caused a situation for condensation but it is for not reporting issue in a timely fashion which could have allowed fixing and minimizing the effect.

Strategically I would try for locations very close to new development so you get the full effect of their coat tails.

The property is in the city of Nashua, NH where you're not allowed to park on the streets and most properties effectively have no lawn.