Caulking for cast Iron Flange Replacement?

1. When I install one of these flange replacements is it useful at all to put some silicone caulk on the contact surface between the inside of the cast iron and the outside of the PVC that goes into the pipe?

2. If a toilet doesn't sit perfectly flat all around and then you shim it, is it good to caulk between toilet and floor (ceramic tile in this case) or just let the gap exist to make it easier to detect any leaks and to facilitate removal of the toilet if needed in future?

3. I've installed a couple of toilets and always wonder how tight to make the toggle bolt holding the toilet to the flange. As tight as you can without breaking the toilet seems to be the goal but how do you know how tight that is? Has anyone ever determined an optimum torque or even a rule-of-thumb?

flange

1. I would not use that flange unless there were some overriding reason to do so. If you have cast iron pipe, I would only use a caulked on cast iron flange.

2. Caulking the gap prevents "things" from going under the toilet, and helps keep it in place, especially if you had to shim it.

3. The rule of thumb is to tighten it enough so it does not move, but not so tight you crack the bowl. Unfortunately, the only way to tell if you tightened it too much is to crack the bowl, you have to use your instincts as to when to stop.

Crack the Bowl

1. Silicone is no worry because you probably can't get this to go in the pipe anyway . You have to clean and wire brush and use ty-seal lube and it may still not go it . I've not used them but plumbers I respect have. There is a mechanical cast iron flange that tightens down.
2. Always caulk a fixture to it's mounting surface. Some do not caulk the very back two inches but I do. Some are using grout.
3. Crack an old toilet you're taking out anyway. You've got to hear that sickening sound when it cracks. Feels like your own bones.

1. What are the problems with the flange I was planning to use?

The reason I was using it for this basement bathroom finish was that my pipe comes through cement floor and there is no space/gap around the cast iron between pipe and cement, the flange needs to go into the pipe. The cast iron replacements I've seen are all "female"-type going on the outside. Is there one that goes into the pipe?

I've slipped it into the pipe and it goes in fine. Maybe because this pipe/toilet has never been used so the pipe is clean. Under these conditions is caulking (outside flange) a good idea?

I don't have a practice/old toilet for the bolts so will just have to use my best judgement.

flange

I will not use an all plastic flange because they will eventually warp, and possibly crack, from the upward tension of the closet bolts. I do not have a lot of faith in a flange that depends on friction to hold it in place because that same upward tension could eventually cause it to move in the pipe. Providing an annular ring around the outside of the pipe is not that difficult with a roto-hammer drill and concrete bit.

The flange is also available in cast iron. I use a wire brush on a drill to clean out the old pipe, makes it a lot easier. You are fortunate that the pipe was clean.

Follow up

I used the Oatey PVC replacement flange that goes inside the pipe. Called a couple of plumbing supply houses and none had a cast iron replacement that goes inside and hammer drilling space for flange on outside didn't seem worth the effort since there did not appear to be any advantage for cast iron on outside. The flange is screwed into the cement floor with 4 screws/anchors. So I don't see how it could warp or cause problems. I did use silicone caulk just for extra measure of seal. No leaks or problems and the Toto Drake is very stable, tight and tight to the floor. By the way that Toto Drake is very nice, I have an HD special in other bathroom that requires 2-3 flushes and splashes all over and is very noisy. Although 2-3 times more expensive it's worth the money.