Toilet drain- is it secured to anything?

I had a 2nd floor toilet leak which most likely is from a failed wax ring.
I busted open the 1st floor ceiling to take a look.

I dunno if I saw clearly, but the abs drain pipe didn't look like it was secured to the plywood underlayment.
I could see the cutout hole in the plywood

How is the toilet drain pipe supposed to be secured to the floor?

 

Toilet flanges are designed to be installed on top of the finished flooring, and anchored through it.

Over a wooden subfloor, deflection can move the toilet and the flange might move independently if things aren't installed properly. The more common reason for a wax ring failure is if the toilet itself rocks. It's most common to need some shims to hold the toilet so it won't rock. The wax is soft but not a spring, so rocking one way will compress it, then when it rocks back, leave a gap.

To help keep the toilet from moving, it also helps to apply sealant around the toilet. This keeps crud from running underneath where it's hard to clean. It can help keep it from sliding, as the anchor bolts aren't perfect at it.

 

Usually it would be glued to the closet flange, and the flange would be screwed to the floor.

 

yeah, i'll have to take a closer look once i remove the toilet.

I can't imagine the plumber would not screw the flange into the floor.

I tried to push the toilet side to side, and it didn't rock. So i'm not sure how the wax ring failed.

 

One potential way is for there to have been a clog below the toilet, and then vigorous toilet plunging. That can develop a fair amount of pressure inside the wax. The fact that water came out might indicate that you have had at least a partial clog.

Since you are pulling the toilet anyway, ask yourself if that toilet is good. Some new toilets flush better and are less likely to clog than older ones, despite using less water. Also consider replacing the supply line and maybe even the stop valve (the water shutoff valve) while you are at it.

 

turns out the problem was that the original plumber didn't shim the toilet, so the front of the toilet dipped down every so slightly every time someone sat on it, even with the caulking. And then the bowl springs back up, leaving a hairline gap where water can flow out between the bowl and the wax ring.

exacerbating the issue was that the flange was sitting 1/4" below the tile floor.

I cut away part of the old wax funnel ring and made it flush to the floor, then stacked another funneled extra thick wax ring on top.

Shimmed the front of the toilet with some pennies, and no leak so far.