Working on an old house, and don't know the history of the plumbing. The soil pipe goes down into a concrete floor in the basement. It drains very slowly. Somebody at one time cut a small oval hole on the side of the pipe about 2.5 feet from the floor, I am guessing it has been cleaned out before. If I use a short snake I just pull up mud. I have been dumping water into the hole for weeks, trying to loosen this up. If I pour a gallon of water in the hole, it will fill up to the hole and slowly, slowly drain away. I am worried that soil and mud in the pipe means the pipe has collapsed under the floor. The pipe goes straight into the floor and I am guessing there is an elbow just below the surface of the floor. If I rent a machine, what types of cutters/ends on the snake would work for muddy clogs? Or any other suggestions? I already tried half a bottle of sulfuric acid, it just foams up the organic matter in the mud and drains away. Help! Thanks.

Have a plumber come out and snake it then run a camera through it and you will know for sure. Otherwise you are just guessing.

You MAY discover you have a problem you never even thought up... pipe that have sunken and now has a dip in it collecting heavier waste matter because stuff doesn't like flowing uphill and will collect until a clog forms. And if that's the case it will happen over and over. Tree root infiltration, collapsed pipe OR a sunken sag in the line would all be detectible with a camera.

As suggested above: Rent sewer video camera from Home Depot and do video inspection first. It will tell you exactly what is wrong with your sewer pipe. Do repairs accordingly.

If your HD doesn't rent sewer cameras, call plumber that has one. Worth every penny.

Dirt in sewer pipe may indicate the pipe is broken, sagged or damaged in some other way. However, substance inside the pipe can also be sludge and that would mean you will have to properly clean the pipe ( water jet it ).

The fact that pipe fills up with one gallon of water means it should be dealt with more-less right away

Hope that helps

Milo