Best way to fix a 1/4 inch drill hole in a 3 inch drain?

If you've got zero play in that stack, trying to use standard solvent weld couplings is going to be a nightmare. You can't slide them far enought back on the existing pipe to drop a new piece in and then slide them back over the joint. Even with repair or slip couplings that don't have the center stop, you're looking at a mess trying to get everthing primed, glued, and aligned before the cement sets in a cramped stud bay.

The move for a vertical stack with no movement is using **shielded couplings**, specifically somethig like a Mission coupling or a Proflex. Don't just use the basic thick rubber Ferncos for a permanent wall-closed repair. They can allow the pipe to sag or shift over time. The shielded ones have a stainless steel band that wraps the whole joint, keeping the pipe ends perfectly aligned and preventing any shear movement. That is what makes it a permanent fix that stays solid for decades. A 6-inch cut is fine, though you relly only need enough space to fit your couplings and a small filler piece. Since it’s a drain and not a pressure line, some guys will suggest a **snap-on patch** where you cut a piece of 3-inch pipe, slice a third of it away, and solvent weld it over the hole. It works, but it can be finicky to get a perfect seal if the surfaces aren't prepped perfectly. If you want that 30-year peace of mind before you hang drywall, the shielded mechanical couplings are much more foolproof. Those shielded couplings are rated for underground and behind-wall use in most jurisdictions. Just make sure the pipe ends are cut square and deburred so the inner gasket seats properly. Tighten the bands down with a nut driver untill they are snug and you'll never have to think about it again. It's way more reliable for a DIYer in a tight spot than fighting a solvent weld that sets in five seconds while you're struggling to force it into place.

I was looking at those Mission couplings at the store and noticed they have specific inch-pound ratings on the bands. Do I acutally need a specialized torque wrench to get them tight enough for a 30-year seal, or is a regular nut driver okay? I’m terrified of over-tightening and cracking the pipe. Also, that snap-on patch thing sounds like a recipe for a hidden leak if I don't get the glue spread perfectly. I think I'll stick to the shielded couplings, but I'm just nervous about knowing when they're actually 'done' and won't leak.

You realy don't need a torque wrench for those Mission bands. Use a 5/16" nut driver and tighten til it's firm enugh that the band isn't moving, but stop once you feel significant resistance. You aren't going to crack Schedule 40 PVC with a hand driver.

One trick: rub a tiny bit of dish soap on the outside of the rubber gasket before sliding the metal shield over. It keeps the rubber from bunching up and ensures a flat seal. Once it's in, run that shower for twenty minutes and check for any dampness with a paper towel. If it stays dry during a long soak, you’re good to close the wall.