I recently purchased a old (1900) 3-family home and during the inspection, it was noted that the drain pipe in the basement went
"uphill" in one section. This issue was never resolved.

At this point in time, the first floor tenant has begun to complain that when the tenants on the top floors take a shower or do their dishes, it backs up their (1st floor) kitchen sink and washer.

I went downstairs to take a closer look at the piping angle problem. It is hard to explain, but I was able to find that the drain from the kitchen sink and washer (from the 1st floor) feed into a main drain pipe that connects to a larger drain pipe. During this section of drain it seems that there was no room to run the pipe any higher because one of the joists gets in the way. I did notice that there was a space ABOVE this joist to run the pipe. If I did this, I would have to angle the drain pipe very steeply in order to feed into the main drain pipe. My question is, do you think this is a good solution or I'm I totally off track. I am not sure it the drain pipe needs to be run at a gradual angle, or can I have a section that is steep. I imagine that no section should run against gravity so the steep angle down would be better than it is now.

Thanks! Chris

First off, the standard slope of a drain line is 1/4" per foot (you can get away with 1/8" if you're desperate). Naturally, less of a slope will lead to problems; however, there is a popular misconception that making the angle steeper than 1/4" per foot will not have any negative effect. This is NOT true. The reason is that if the angle is too steep, the wastewater will flow downhill too quickly, leaving the solids behind. So the easy way out (making the pipe extremely steep) may not be the best way out.

Now, before we discuss the angle of your pipes any further, let's take a look at some of the important underlying details. Iit sounds to me that the problem is actually due to a clog in pipe, not simply the pipe angle itself. I say this because even though it's "uphill", wastewater WILL make it over the "hill" and into the rest of the pipe the same way the water in a p-trap manages to climb out (i.e. the first few gallons will settle in the bottom of the problematic angle, but once the water level reaches the top of the faulty section, any water added will "overflow" the crest of the "hill"). In other words, essentially what you've got is a giant p-trap.

A clog is especially likely (in fact, almost guaranteed) at that point in the pipe, since even though liquid waste will easily flow over the "hill", solid waste will settle to the bottom of the "valley" in the pipe (similar to the way it settles to the bottom of a septic tank).

In summary, my humble opinion is that this problem is indeed caused by the pipe angle - indirectly, that is; the angle is causing a clog to build up. So why am I telling you all this - what difference does it make, if you're going to have to fix the pipe either way? Simple: until you fix the pipe, my advice is to snake out the drain line. Like this, at least it'll work temporarily until you fix the pipe.

As for fixing the pipe, would it be possible for you to post some pictures so we can get a better idea of the situation? Whoever said "a picture is worth a thousand words" wasn't kidding, you know. ;)

Let us know what happens.
Moishe