Help with large cast iron toilet flange

Question

Flushed the toilet last night and found water seeping from the side of the toilet at the floor.

I removed the toilet to investigate. I found there were two wax ring doubled up. Cleaned all the wax off to get a look at the flange. The house was built in the 1950s with cast waste drain. Measured the drain opening and it come in at 5 inches. With all the wax rings I could find saying they are good to 4 inches I picked up a Sioux Chief push tite flange to hopefully solve the leak going forward.

I pressed in the new flange to test fit and see how much it sticks out of the floor. With new flange it is sitting 3/4 inch above the floor. Which I know is way too high, toilet will never sit on the floor with this.

Can I cut off a bit of the cast drain with an angle grinder until I can get the new flange sitting 1/4 inch off the floor installed?

Answer 1

Some ideas:

• Use a Fernco rubber bushing (donut) and a 4" PVC stub to standardize the diameter a bit. Here are some photos in a discussion thread. That person used polyurethane caulk, but I'd look for a rubber bushing for more stability and a more reliable seal. Fernco also has their own wax-free toilet seal that may work, but I don't see one for a 5" bore.
• Purchase a dedicated product other than a wax ring such as Sani Seal (with which I have no personal experience, but it's mentioned in the thread above).
• Replace the flange (if you have access from below). It's not terribly difficult to cut cast iron and extend with PVC or ABS.

To answer your question about cutting the existing flange... you certainly can, but getting a good seal may be challenging with parts that weren't designed for that situation. You'd need to be sure that no sewer gas leaks around the new flange even if waste doesn't escape due to gravity.

You'll also need to be sure that it's secured to the subfloor well. There can be a lot of force on a toilet and you don't want it pulling free.