At the end, we feel very uncomfortable confronting him about the junk/trash and parking lot issue.

As I reach the bottom and turn to the sounds source, I am confronted with downpour of water coming from the ceiling of the basement bathroom.

I would find an eviction lawyer and then bring things to a head: confront the boyfriend with a list of violations and say that if there are any more the next thing he will hear from you will be an eviction notice, no negotiations.

Then if there is evidence of people there other then tenants , confront the tenant

That way, you are not being confrontational, but leaving things open should they want to come down in the near future.  

As best as I can tell, the only benefit to not telling a tenant you are the owner is if you are wishy washy and afraid of confrontation.

It sounds like when you talk to them on the phone and explain what you want they are not that interested.Some brokers/agents and even buyers avoid confrontation so hope when they ignore people they will go away naturally on their own.If the broker/agent perceives tons of work and time involved for a low return they tend to run away.Example if I had a commercial investor call me for retail value add at 1 million purchase price I would politely decline.

As long as you screen well, and if stuff comes up that needs addressed,  ie not paying rent,and you don't mind the confrontation, do it.  

When I confronted the tenant, their response was "It's just a small bird, not a cat or a dog".

Now that I'm considering selling and moving the money into syndications, I'm confronted with just biting the bullet and paying the tax and the deferred taxes.