closet flange problem

I am working on finishing my basement bath (concrete floor) and I set the closet flange today (PVC with a stainless steel ring). The problem is that the flange does not sit perfectly flat on the floor, it is flush in the front but the back is raised up about 3/16 of an inch (it is however level side to side). When I grab onto the flange and try and move it around it is rock solid. I'm thinking that the reason is because of the 1/4 per foot slope on the waste lines. But being that the pipes are encased in concrete there is absolutely no give there to get it flat. I put my wife’s best fire engine red lipstick on the high side of the flange set the toilet on top and wiggled it around. There was no transfer to the bottom of the toilet, so at least it's not holding the toilet up off the floor. My thinking is to just put some hard plastic shims under the flange and set the toilet in wax and hope for the best. I would appreciate any input from you guys... thanks for you time!

I've been downstairs looking at it and came up with some usefull informaion ... I determined that there is at least 1/8 of space between the top of the flange and the bottom of the toilet. By putting a piece of 1/8 shim stock ontop of the high side of the flange and there was no rocking. When I added 2 pieces of shimstock there was rocking.

Most likely the riser coming out of the slab isn't perfectly plumb or level like it should be. 3/16" isn't great, but you can work with it. Just shim as necessary and anchor that flange down with tapcons.

flange.

You don't need shims, and the flange is offlevel because the installer did not plumb the riser, NOT because of the slope of the pipe.

Any suggestions on working with it? Will one type of wax ring work better than another?

And just out of curosity how would you plumb the riser under a slab installation like that without bending the waste line? I guess you could use two street forty five's that were slightly offset but I would think that would casue more problems with flow and snaking?

You're making a mountain out of a 3/16" molehill. The flange only serves to anchor the toilet -- it doesn't support it (if it does, you do have a problem).

If the toilet sits flush to the floor all around, you're good. The wax ring seals the gap between the horn on the toilet and the flange, and an extra 3/16" on one side isn't going to make a difference (unless your finished floor height is well above the flange, in which case you use a thicker wax ring, or double it up).

As long as there is a gap to seal with the wax, and the toilet is not held up because the flange sits too high, you'll be ine. A regular wax ring is all you need...no funnels, not extra thick...just a regualr $.99 version (well, I haven't priced them in awhile!).

The hubs are made to account for the slope, so a 90 into a hub isn't really a 90 as there's a small offset to account for the slope.