Is it safe to drill into the wall directly above my toilet for a cabinet?

The vent stack is almost always centered directly behind the toilet, so if you're planning on drilling right in the middle of that wall space, you're likely to hit a 2-inch PVC pipe. Since you have an attic above you, the easiest way to confirm this is to climb up there and look for where the plumbing vent exits trough the roof. If you see a pipe sticking out of the roof right above the bathroom, you'll know exactly where that vertical line is running inside the wall.

You realy want to focus on finding the **studs** rather than just avoiding pipes. Most plumbing and electrical lines are run in the cavities between the studs. If you use your magnetic stud finder to locate the drywall screws, you can map out exactly where the wood is. Measure for standard 16-inch spacing to verify you've acutally found the studs and not just a random metal plate. If you hit somethig hard while drilling your pilot hole that feels like metal, stop immediatly; that's likely a protector plate meant to keep you from puncturing a pipe or wire. Another trick if you're still nervous is to run the hot water in the sink for a few minutes. If you have access to a cheap thermal camera or even a non-contact infrared thermometer, you can sometimes see the heat signature of the pipes through the drywall. But usually, if you stay centered on the wood studs and don't drill deeper than about an inch and a quarter, you're perfectly safe.

If your water lines come up through the floor, you're mainly just dodging that vertical vent pipe and maybe some electrical for the light fixture. Electrical wires are usually stapled to the side of a stud, so as long as you're driving your screw into the **center** of the stud, you won't have any issues. Just take it slow with the drill and don't force it if you feel resistance.

Honestly, I'd just poke a tiny hole with a finish nail first. You can feel around with a bent coat hanger if you're realy worried about that PVC. If you hit somethig solid that ain't wood, you'll know pretty quick.

Also, don't go ham with the power drill. Use a handheld screwdriver for the last bit. You'll feel the resistance change way before you acutally pop a hole in a pipe. If it's an older place, just be extra careful 'cause you never know what kind of DIY mess is behind that rock.

I had this exact worry last month. What worked for me was using a thin piece of wire—like a guitar string or thin floral wire—pushed thru the pilot hole. If you can push it in three or four inches without hitting anything, you’re golden. Also, check the base of your toilet. If the flange is bolted down right in the center, that vent is almost certainly dead center too. I just offset my cabinet by two inches to hit the stud and avoid the 'danger zone' entirely. Better to have a slightly off-center cabinet than a fountain in the bathroom.

Grab a Walabot DIY 2 if you want to acutally see what's back there. Most modern builds use a 2x6 wet wall for the throne to accommodate a 3-inch DWV stack, giving you a little more clearance than a standard 2x4 partition. If you're using #8 or #10 wood screws and only going 1.25 inches deep, you're ussually safe. Just watch for any PEX lines that might be notched into the studs—builders love to get lazy there. If you hit the king stud about 7-8 inches off-center, you’re almost guaranteed to miss the main vent line entirely.

Spot on about checking the attic. If you do go up there, check if there's an electrical junction box or a wire run for that light fixture you mentioned. Sometimes builders will staple a Romex line horizontally across the studs to get from the switch to the light above the sink. If you're mounting a wide cabinet, you might cross its path even if you're hitting the studs. I always pull the cover plate off the nearby outlet or switch and peek in with a flashlight to see wich direction the wires are headed before I start drilling.

Quick update — I took the advice to check the attic first and found the vent stack was shifted way further left than I thought. I used a finish nail to double-check the spot and everything felt clear. The cabinet is up now! Thanks for the tip about the handheld screwdriver, it definitely helped me feel for any resistance.