Plumbing in toilet flange

Im laying tile in a bathroom using subfloor plus 1/2 inch plywood then backer board. I have to connect a new abs toilet flange to a new piece of 3 inch pipe. I had to cut a portion of the old pipe out from below to remove flange.
My questions are
1 is it true the flange should go on the new tile. What do I use to secure flange to subfloor through tile
2 when I cut the pipe sticking out of the bathroom floor how high should it be above the floor before I cement the new flange in place or should the waste pipe be flush with floor before gluing on flange

As an aside because of lack of space and wires etc in basement - i had to use a very short piece of pipe between a coupler an elbow. In fact when I glued them you can barely see the pipe. Looks just elbow then coupler. I I think I have one inch of pipe in the coupler and one inch in the elbow. But not seated all the way. But more than 1/3. I I If this is bad I will need to do some demo work in basement and start again.

Yes, the flange should be installed on top of the finished floor, and anchored through it into the subfloor. The easiest way to prevent having to drill through holes in the tile is to notch them with your tilesaw first. The stackup of fittings may dictate certain ones. As to how high to cut it, if you choose the right flange, one without an internal hub, you can slide it over the pipe, and, after the cement sets, cut off the part that sticks out.

quote; As to how high to cut it, if you choose the right flange, one without an internal hub, you can slide it over the pipe,

I have NEVER used a 3" riser or flange, but I have also NEVER seen a 3" flange without an internal "stop" to prevent it from sliding down the pipe.

Thanks for your help

It's a flange that stops on the pipe. It has a knockout to remove before installation to keep sewer gas from coming in. Dumb question but it will work with any toilet right? Also what kind of screws should I use to get through the plywood, tile and cement backer into subfloor. My plywood and backer adds an inch on top of my subfloor And I don't understand what is meant by notching the tile for the screws.
Before I install the flange do I cut the pipe flush with floor?

If you mark the tile where the holes in the flange will be, before you set the tile, you saw a notch there so that you don't need to drill holes through the tile - the screw goes through the notch. The better flange is one with a SS (not painted steel) ring around it, rather than one that is all plastic. You want to use ss or brass screws to anchor the flange. You'll need to measure the depth of the socket to see how high the pipe needs to be to get the flange to sit flush on top of the finished floor once it is glued. It is unlikely you'll be able to dry fit it, as the joint needs the cement to melt the surfaces to make it fit. This is referred to as an interference fit.

Cutting the pipe 1/8-1/4" below the finished floor will allow the flange to glue up fine and set tight to the floor. The bell on the flange is deep enough that you have some leeway, but if you leave the pipe too long the flange will not go down tight to the floor.

Drilling with a diamond bit works fine on most tile. Run it slow and keep it wet so that the bit does not get hot.

I also recommend the flange with the stainless steel ring, as it allows you to rotate the ring into position AFTER cementing the flange in place. With an all-plastic flange, you only get one shot to make sure the holes for the WC bolts are lined up perfectly.

YOu cut the pipe WHEREVER the flange requires it to be when the flange is on TOP of the tile. Some you cut it even with the floor, some 1/2" below the top of the tile, and others flush with the top of the flange. Yours has a "pipe stop" so you have to figure out WHERE that point will be and cut the pipe appropriately.

cacher_chick said:

Drilling with a diamond bit works fine on most tile. Run it slow and keep it wet so that the bit does not get hot.

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This certainly works, and I've done it that way, but it is one more thing a DIY'er may not have or ever need again, you do likely have a wetsaw, so that's why I recommended notching the tile for the screw clearance. Whatever you do, make sure there is enough clearance around the faster - you don't want it tight in the tile or you risk cracking it. Some tile is VERY hard, a good porcelain can be close to diamond. Some tile is fairly soft, and a carbide tipped drill will cut through. A wetsaw will cut basically anything.

As far as what screws to use, my personal choice is #12 stainless steel of sufficient length to go all the way through the sub floor. Four screws is probably enough. Theoretically, there should never be water on those screws so any steel would work. However, since they are out of sight and you want them to last virtually forever, I feel the peace of mind having the stainless steel is worth extra expense.

I'm suprised theres no debate about whether to set flange at finished floor level or on subfloor. Usually is. But I wanted mine at finished floor level.

After tile installer laid my tile....I bought the Bosch tile drill bit set from Home Depot. Set flange , marked holes, drilled thru tile with tile bits and like Gary said used #12 screws to firmly set flange flush with floor.

Before I drilled holes thru tile, I used some playdough to form a small circle around marks. Filled circle with a little bit of water to keep bit cool while drilling. Worked fine..

quote; I'm suprised theres no debate about whether to set flange at finished floor level or on subfloor. Usually is. But I wanted mine at finished floor level.

There is NEVER a debate about that if you want to do the job correctly. The debate occurs when someone DID put it on the subfloor and then wants affirmation that it is "okay". "At finished floor level" is also a vague term. Do you mean "level" with the floor, or "on top of the floor"?

I hope that pipe slopes downward.....can't tell in the photo.

hj said:

The debate occurs when someone DID put it on the subfloor and then wants affirmation that it is "okay". "At finished floor level" is also a vague term. Do you mean "level" with the floor, or "on top of the floor"?

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I agree. Most that argue or debate have it on the subfloor and want affirmation that with stackers and double wax rings it will be OK. Anyway by "level" with floor I meant that the bottom of the flange is firmly seated on the finished floor so in your words, "on top of floor"

jimbo said:

I hope that pipe slopes downward.....can't tell in the photo.

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Yes it slopes. And it even has a vent. Drug up an older photo #3.