Ok to screw flange/toilet to plywood?

Hello Experts,

Drilled a couple nice holes through tile and the 2" mudbed underneath. Below that is plywood. No idea how thick but from a test hole it looks like 5/8" or 3/4". Is it ok to screw the 5/16" screws to hold a toilet into that plywood? If yes, what diameter pilot hole do you guys drill?

In our case it's a floor-mount rear-discharge unit but I guess the same would go for securing the typical flange of a normal toilet since a flange holds the whole toilet via its bolts.

Putting a brace underneath this one would be a bear. I'd probably have to lose 30 pounds or more just to be able to crawl to that spot.

Regards, Joerg.

That's the way flanges are attached to the floor. As far as a pilot hole for the screws is concerned, I'd use about a 3/16" for the 5/16" screw and then use a power driver to sock 'em down. The length should penetrate the sub floor since you have so much above it, so at least a 3" screw.

Thanks, Gary. So I assume the plywood provides enough "meat" to anchor down things like toilets. I grew up in Europe where there is no wood in houses (except for the rafters and furniture), that's why I asked.

It's more like 5" screws in my case since the toilet base thickness adds 1-1/2 to the 2" of mudbed, plus tile. The amazing thing is that you can get stuff like that at the local ACE store. No need to drive into town.

Regards, Joerg.