Costs could vary wildly from $10-30/cy, and would be dependent on a number of factors...permitting, disposal site for dredged material, hydraulic vs mechanical, etc. 

Ie: should I have plumber replace valves, pluming hoses, etc; 3.

If I can help it,I only buy units with all utilities paid by tenants.When I started out,I got an older duplex with a shared meter.Have not repeated the mistake since then.6 months ago,water bill at that unit jumped from 45$ to 2000$-in one month.Then it stayed that way for three billing cycles before I caught on to it.Turns out the neighbor had connected a hose pipe to the backyard pipe while tenant was away and started running a car wash on my dime.When informed,tenant was essentially nonplussed.Not her business.

any pictures I've seen of lines coming through the foundation show two lines. this looks like a hose to me?

BBQ Nat Gas hoses have quick connects.....like a air compressor.

I've gone from zero to 5 multiple unit buildings in the last 12ish months...and every day feels like a new challenge and something new to learn.   I'm continuing to learn and looking to expand opportunities, investmen...

I roll my eyes when some dude with a pressure washer thinks he is worth 300 bucks for 3 hours of work holding a hose.  

Hook up a long hose from their outdoor water faucet to a water faucet on the home.  

From your post I can see that you are experienced investor and that there is a good chance that in near future you would buy another duplex or maybe flip a hose.

The latter are "drinking from a fire hose", as they say, with lots of info flying in their face and which atoms of information are useful to themselves is hard to determine.