Re: That Darn PO!!
I work with poly tanks a lot, including the Ronco's. I install fittings up to 12" in tanks up to 12,500 gallons, thats 142" diameter x 16 feet tall! Currently working on a job with 6 12,500 gallon tanks, one 900 gallon, and four 65 gallon, all of which we will install about 30 fittings into.
If the tank doesn't have an inspection port, now is the time to install one. Once you have a port big enough for the flange of a bulkhead fitting to pass through you are all set. All you have to do is trim the spin welded fitting off flush with the outside of the tank using a coarse hacksaw blade. Then enlarge the hole to take the neck of the bulkhead fitting. Use a tape measure to reach across the tank to the hole, and slide the bulkhead down the tape measure into the hole from the inside. Don't forget the gasket! Then install the nut on the outside, and your tank is now better than new, because that bulkhead is removable and replaceable if it gets damaged, unlike the spinweld fitting.
Look at Hayward or Spears bulkheads, and get the EPDM gasket for potable water. Buna is fine too.
Gary H. Lucas