Installing Toilet Flange in Basement Bathroom

The flange should sit on the finished floor.  Too low and you'll need to use a thicker wax ring which can increase the chance of a leak, too high and the toilet will wobble.  Measure carefully and make sure you include the thickness of your thinset.

Just use ordinary concrete, which you can buy in bags.  Remember that while extra water will make the concrete easier to work with, it will decrease the strength of the mix and increase the chances of cracking.

Since you'll be filling with concrete it's probably not necessary to screw down the flange.  If you want to, use plastic anchors and stainless screws or masonry screw (e.g., Tapcons).

The flange I have fits inside the 3" ABS pipe coming up.  Should I check the height and then glue it together before I install the tile floor?

Is there any way I can avoid having to drill through the tile floor to secure the flange?

THANKS!!

If you have a stub coming up, then I'd just leave that.  Once you have your floor down cut off the stub and drop on your flange. Since the stub will be in concrete, you probably don't have to screw down the flange.  You just don't want it to move.

Remember too, there's a waiting time before you can set tile over fresh concrete.  Of hand, I don't know what it is but you don't want your tiles to pop.

The toilet flange is supposed to rest on top of the 'finished' floor...That way all you will need is a standard wax ring to make a water and gas-tight seal. If you are going to add a ceramic tile and an underlayment then you will need to raise the flange above the sub-floor by 3/4"...You can find a product (spacers) on Amazon called Set-Rite or at their website and watch the YouTube video they have there that will explain everything you ever wanted to know about toilet flanges but were afraid to ask!!