Welcome to my humble commode.

So last weekend my S/O discovered a tile (one) that needed repair in our bathroom. You'll notice the floor in this photo is nice and clean, and doesn't share the muted yellow color of the 1950s subway tile on the wall. Well it wasn't always like this.

One loose yellow tile led to another, until I found I could scoop them all up with a shovel...

That's literally just the grout keeping the beehive shaped plates of woe together, but this was only the beginning of my troubles.

Got closer to the toilet and found I could put my finger into the mush that once supported the tiles. So I began removing the compost formerly known as floor.

Only thing that was ok was the subfloor since there was a layer of that paper between it and the interior floorboards. Didn't have any tar paper so garbage bags will have to suffice.

Next a layer of 7/16 OSB brings it to the 1/4" ply overlay that the old tile was stuck to.

Add my own layer of 1/4 inch ply (a little scant because they want that Dolla y'all) and the vinyl tile brings it back up to zero. Note the grey ring around the the toilet drain. Yes, thats an old lead riser that would normally be soldered to a brass flange ring that wasn't there. ( thanks, @ifitseasytakeittwice )

My first toilet install went ok. All the leaks were on the clean side, so I'mma call that a win.