We have a clogged main drain, our clean out is in the basement.  

I have a 12 unit that is a real money maker and I'd love to find another one-I have duplexes too; but they just don't offer the same margins.Given your PM knowledge you should consider jumping in deeper than a 4 plex; it does not have the economies of scale that a single building with 3x units gives you and it will drain your available cash thus making a bigger better deal more difficult, maybe impossible.

Based on what you have done already I am guessing you like the long term appreciation and cashflow approach to real estate investing.I dont have any information on how you acquired your other properties or what your financial position so take my advice as "what I would do" advice.You just bought a home that you put down between 5-20% so it probably drained you a bit.

Not clear if this covers drain or only supply. 

In the other two instances, the city had put pumps that led from the creeks straight into the storm drains and that took care of it very well.

I feel even though they did spend ~6 hours between the two plumbers, that a competent plumber would have got that drained cleared via the roof in less then 1.5 hours. 

Property A and B are lake lots next to each other and Property A is now foreclosed on.Property A - 1/2 acre lot, with a tear down home on it.  10 year old septic/drain field for this home is on Property B, which original owner still owns next door.Property B - 1/2 acre lot, 5 year old garage on it.  

Bull has been out in drain field area of yard etc and there are huge prints everywhere.

Hire a qualified plumber to send a camera through the stacks and main drains before purchasing the property.

I've had to replace the water and drain lines on all my multi-family properties, for example.Also, separating the meters will be extremely expensive.