How to Use a Grinder to Replace an Old Clay Sewer Main Tap

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If you live in an older town, more than likely the sewer mains are terra cotta and at least 6 inches in diameter. A chain snapper is ideal for cutting a main, but most mains are too large to implement that tool. Here’s a look at the “grinder method” for replacing an old clay sewer main tap.

The Trench

Do not attempt to get too close to the main. Hitting a sewer main (depending on how “busy” the main is) without prepping the ditch can be a nightmare.

Once you have dug a trench to accept the new lateral, you’ll be digging in the area of the tie-in to the main sewer. Turn your excavator in line with the main instead of in line with the lateral. Now dig a trench that gives you plenty of room in terms of both width and length. Make sure you leave enough room to fit shoring in the trench in order to protect the workers. Keep in mind that the trench box should sit flat in the bottom of the trench and the top of the trench box should extend above ground level so as to prevent any debris from falling in. Lastly, dig a large sump hole next to your work area, which will give the waste a place to go in order to get pumped out.

When you have exposed the top of the sewer main as well as some room on either side of it, it is time to set the shoring in the trench and dig the sewer main out by hand. You really want to expose the old wye fittings plus additional room both upstream and downstream since the new tap (PVC/ABS) will take up more room than the clay fitting did. When you dig around the main, make sure you get it completely dug out and clear, even underneath the piping. This will help tremendously when you go to cut the main and slide your new piece in.

Getting Set Up

When you cut into the main sewer line, waste will be entering the ditch with you. How “busy” that specific line is at the time of your tap will determine how you get set up. The overall goal when tapping the sewer main is controlling the flow of waste. The only real way to know how busy the main is is to take a grinder with a diamond wheel and cut a window in the top of the pipe. After you score a small window with your grinder, tap on it with a hammer and pull it out. If you are concerned about it falling into the main, drill a masonry bit and barely screw in a Tapcon screw to hold and pull the rectangle up and out. 

Once you have exposed a length of the main and the old clay sewer tap, you need to assemble the new branch piece up on dry land. You want to have this piece ready to go before you cut into the main. Having this piece ready to go with Fernco couplings on will make the slide-in process much easier. You want to have enough pipe on either side of your wye to be able to completely slide on your Fernco so that you can simply slide the new piece in and slide the Ferncos onto the upstream and downstream clay main. Take the tightening bands and the nonshear bands off both Ferncos to make it easier to slide on. Get a measurement of your new piece end to end and add an inch to that measurement. Return to your trench and mark your cut spots.

To set up your pumping system, first decide what kind of pump you are going to use based on how busy the main is. You also have to find a place to pump the effluent. Most times you can pump the sewage into a downstream manhole. Use your best judgment on where to pump to, but make no mistake — you should have a sump hole dug with a pump in place and a place to pump to. Even if it looks like an easy repair, you never know what could happen.

Cut Out and Replace

Cut the upstream side first using a grinder. You will have to cut out about a 6-inch section in order to get your grinder down far enough to cut the bottom of the pipe. Wear a face shield, thick gloves, a dust mask, and hearing protection. Have in the trench with you a hammer, 5/16-inch nutter with an impact drill, a few clean rags, and a few blocks of wood or bricks. Once you have the upstream side cut, move down to cut the downstream side and slide your waste piece out and discard. Take your already glued and assembled new piece and slide it into place moving the Ferncos onto the old clay piping. Now put on your bands and tighten.

Lastly, you should put some blocking underneath the new piece for support and pour some concrete underneath the new piece to prevent it from settling.

About the Author

Anthony Pacilla is a registered master plumber for McVehil Plumbing in Washington, Pennsylvania. He has 22 years of experience in the plumbing and HVAC trades, and has a bachelor’s in business and economics from Thiel College. 


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