If you can manage the payments, it could be a good idea to hold on to it until prices raise and you can sell for a profit.

Even with rates where they're at lenders require you to have a certain ratio on the payment of rent vs mortgage.

Without tying up all my cash, what avenues should I pursue to cover the $72,400 cash payment I will need to make the deal happen on top of taking over the current owners loan?

You're probably buying at higher rates, but just run the numbers, see what you can afford, and compare potential monthly payments to what you could get in rent.

1) make the payment directly from my HELOC account2) transfer the money from HELOC to business checking account, and then make the payment from my business checking account.

The payment is $2,196 with my current insurance.

“In the UK ‘more than a million households will see a significant jump in monthly payments’ this year as ‘the next batch of UK homeowners to have their mortgages repriced are preparing to make personal sacrifices”(Bloomberg).

The lot doesn't generate cash flow so it does not throw off any money to make a payment with. 

We use the RHAWA lease agreement, if you are not a member of that organization or WLA, I would recommend you sign up.In the RHAWA lease agreement (not Seattle specific), it states that security deposit can be used all purposes including unpaid rent, damage, cleaning, late payment, utilities, keys and other charges.It is never a bad idea to pay for an hour of an attorney's time to go over any of these concerns and then you can be confident you are following the law.

Protect that down payment money.