Underground Toilet Installation

Locate the toilet flange on the bathroom floor. The flange is a raised circle with a flat cover plate on top of it; it is within 1 foot of the wall. The flange connects a toilet to the drainpipe that services the toilet. Remove the cover plate on top of the toilet flange with a screwdriver, and set it on the bathroom floor. Stand the two floor bolts sticking out of the flange straight up, shifting them into position by hand if necessary.

Turn the bowl portion of a gravity-flush toilet upside down. Pick up the wax ring that came with the gravity-flush toilet installation kit; the wax ring is usually a pale or yellowish color and about a hand span wide. Slide the wax ring onto the toilet horn, which is the circular protruding portion that extends from the toilet's bottom. The horn has a slightly smaller circumference than the toilet flange in the floor. Slide the toilet sleeve onto the horn, between it and the wax ring. The toilet sleeve is circular piece of metal or plastic that is taller than the wax ring.

Lift the toilet bowl off the floor, and turn it right side up while it is still in your arms. Take it to the toilet flange. The two floor bolts need to slide up and through the holes on each side of the bowl's base. Lower the bowl straight down and over the floor bolts.

Grip the sides of the gravity-flush toilet bowl, placing one hand on each side. Press down gently, compressing the wax ring against the flange until the bowl is flat against the floor.

Slide washers and nuts over the floor bolts. Tighten them with an adjustable wrench.

Turn the toilet tank upside down. Take note of the spud washer’s location; it is a thick, black ring a few inches in diameter and flanked by two bolt holes. It is typically located in the center of the tank. Lift the toilet tank up, and place it on top of the bowl. The spud washer fits into the water inlet opening at the back of the bowl. When those elements are aligned, the holes for the tank bolts in the bowl and tank also align.

Insert the tank's bolts down through the tank to the bowl. Use the wrench or your fingers to tighten the washer and nuts from beneath the bowl.

Attach the water supply tubing from the installation kit to the water supply valve on the wall and the fill valve on the toilet tank. Tighten the coupling nuts that hold the tubing in place with the wrench.

Apply a bead of silicone caulk around the toilet base where it meets the floor to seal the location. The toilet should be flat on the floor.

Install the toilet flush mechanisms and seat according to the manufacturer’s instructions.