the house I bought a few years ago has a rental tank, I didn't know it was a rental until about a year after we moved in. DE doesn't have my name, the bills still come in the old owners name. I have never paid them a dime...don't really know if I am on the hook or not...
I can answer that one.
You are.
Remember when you bought the house and you went to sign the papers at your lawyer's place? You probably (like most of us) didn't even bother to read what you were signing then. Somewhere in all that mouse print and legalese was a requirement that you would assume the various rentals on the place. At the time you signed, it would have been the time to tell the previous owner that you would not assume the lease on the tank period.
Now that said, if you've fallen through the cracks, you are laughing.
(I fell through the cracks with Bell Telephone once and had free internet for 9 years before they figured it out. When they did, I just said, "I dunno" and that I would pay them going forward. They seemed happy with that.)
If I was to buy another house and it had a rental tank in there, I would refuse to assume the rental agreement right out of the gate. I would remove the old tank, put it in the back yard and tell DE or Enbridge that they had 48 hours to pick it up orelse I would be scrapping it and sending them the bill for pickup. (Odds are they wouldn't even pick it up.)