Installing a toilet in a new basement bathroom. Center of 4: PVC drain pipe is 13.5" from the wall, so I tried to use an offset flange, made by Oatey Caspers. It was a snug fit, so I did some sanding with sandpaper and emery cloth, applied the cement and tapped it down, but could not get it in all the way, then had a tough time removing it (in pieces). I also have a straight flange. The straight flange unit will fit nicely into the 4" drain, but the offset flange unit is about 1/16th" wider, just enough to prevent it being seated all the way in. I checked Home depot and went through all their offset flanges and selected one that appeared smallest, but it still won't fit.

It seems like a defect in the flange, or is it possible that another manufacturer would have a tighter tolerance on the outside dimension? I'm reluctant to sand it down by hand, in case it ends up uneven and I don't get a good seal.

I'm tempted to just use the straight flange, and have the back of the tank 1-1/2 inches out from the wall, but it wouldn't look the best. I want the flange to be flush with the concrete floor.

Any suggestions would be appreciated. Also, the concrete floor is a bit uneven where the drain pipe is located. What's the best way to shim the toilet and/or the flange? Plumber's putty, rubber shims, or ?

Good morning Chris,
Let's see if another offset flange will work. Go to a plumbing supply house or plumbing shop and ask for a 4 X 1 1/2" PVC offset toilet flange.
Make very sure that you have all the glue sanded off and removed from the pipe. Sand everthing down if it fits too tight but don't try to force the flange all the way onto the pipe as it is slightly tapered and will bind.
Prime both the inside of the flange and the outside of the pipe with PVC Primer and apply PVC cement,(glue) to both pieces. Position the offset flange and press down to the floor. Don't wory about getting a good seal. If you primed it correctly the cement will melt the PVC and weld the two pieces together.
If the toilet bowl rocks or is uneven after you tighten the closet bolts it must be shimmed and leveled. Go to a plumbing shop and ask to purchase a small tub of White Dap Tub and Tile caulk and soime scrap sheet lead
from roof flashings. Cut the lead into strips a few inches long and 1/2" wide.
Loosen the closet bolts until the bowl loosens down and fold the lead strips to fit snug pushing them in until they're even with the bowl and not sticking out. If you loose one under the bowl just leave it or hook it out with a clotheshanger. Retighten the closet bolts and try to rock the bowl. If it still rocks a little then loosen down and shim the low spot. After you get the bowl set run a ring of White Dap around the base of the bowl and the floor. Smooth it out with your finger and wipe the excess oiff with a damp cloth.
That should do it. Good luck, Tom