I purchased a triplex in CT back in February of 2020 and I've been house hacking it. I inherited two sets of tenants, one couple up stairs in the 2 bed unit and one right beside me in the other single bed unit. All leases expired when I purchased properties, rent rolls looked solid so I wasn't too concerned. I put upstairs tenant on month to month lease due to concerns relating to COVID19 and the tenant next to me has not been in a lease since April of 2021 when his previous lease expired from former owner. (Had zero luck getting copy of that lease before purchase and I tried.)  So today the tenant moved in a 15 lb dog that's old and has health problems. All day while woking from home it's barking, wheezing and crying bitterly. I addressed the rogue visitor with tenant when I encountered him outside by chance. (I am the property manager btw, not the landlord... *cough so I was friendly and asked why was there a dog in his unit? I reminded him gently that per our conversation earlier in the year (when he asked what owners stance was on pets) I flatly told him the owners do not permit pets. 

I told him that I'm on his side and I wouldn't say anything to owners for a few days but after that he would need to find a place for poochie to call home. Otherwise it's my responsibility to tell owners of an unauthorized animal in his possession. He told me "well, do what you gotta do man" I asked him what he was going to do, he said "well I'll move" I replied and said that will be his only option if he attempts to keep the animal in his unit. I encouraged him to find another solution for the animal and that the owners would be very sad to see him have to leave. I asked him about his lease, "I'm not on one" he replied. I explained that means he is on a month to month lease by default and that likely he will be given the 30 days to quit possession should he choose to attempt to keep the animal at this property.

Rent is below market, he is paying only $600 for a $725 unit. I kept their rents low throughout COVID19 to create goodwill but back when I closed they were told rents would increase in 2021. He smokes a lot, sometimes inside his unit but he masks scent with incense that makes my entire property smell like a casino.  SO lets recap, he is not on a lease, I have no idea what his previous lease from previous owners said about pets. (I'll bet it was NO on that previous lease because otherwise this guy would have had a dog when I purchased the place, I have no doubt.)

I know I probably made a ton of mistakes here, please go easy on me this is my first property ever.  I don't want the dog here. What would you do?