Bob,

A toilet I have in my house keeps getting clogged up

Most clogs are due to excessive paper use and/or flushing items that
should be thrown in the trash.

ripped up the floor boards (it is on a second floor) and I followed
the toilet 3-inch toilet drain pipe line. To my dismay, before taking
a vertical drop, the drain runs 15 feet. The drain is well ventilated
after about 9 feet and is at a steady slope of only 1/4 inch per foot.
I replaced the drain pipe, but there was no damage to the original
one so I don't think that will help much. I built a 1.5 inch pedestal
below the toilet to slightly increase the slope. Even though this is
at-or-above the 1/4 inch per foot slope minimum, is this 15 foot
horizontal drain setup "up to code"?

The last code I dealt with specified 6 feet as the maximum distance
between the closet flange and the vent. This was for UPC, I believe IPC
allows up to 12 feet. So, I doubt the 9 foot distance to your vent would
be too much of a problem.

If you have room in the joist space, you could add a "Y" in the drain
line to add a vent closer to the toilet that runs horizontally above the
drain line and tie into the regular vent at the other end. Probably not
necessary, but it may be an option if you're worried about it.

I wouldn't go any steeper than the 1/4" per foot slope. The liquids will
rush down the pipe faster, potentially leaving solids behind to cause a
clog. Many of my drain lines are about 1/8" per foot slope, and they
drain well.

If you had 4" pipe, I would have suggested switching to 3" pipe with a
low-flow toilet. The lower quantity of water can spread out too thin in
the bottom of a 4" pipe to carry away the solids. But, it sounds like you
already have 3" pipe, so that shouldn't be a problem.

Assuming the toilet is the only fixture you are having trouble with, I
suspect the drain is fine. You may want to focus your attention on the
vent. Go up on the roof and check the vents. Run the garden hose down the
vent and/or run a snake through the vent. Sometimes they get clogged with
leaves, birds nests, bee hives, or whatever. Trying to drain a toilet
without a vent is like trying to pour liquid from a can with only one
hole. It'll go "glug-glug" instead of flowing smoothly.

If you live in a cold climate, your roof vent should be at least 3".
Smaller vents can ice over when the moist air leaves the vent, eventually
blocking the vent. If your vent is smaller, you can replace the current
vent with larger pipe and transition to the smaller pipe in the attic
(the closer to the heated space, the better). I'd also install a
"mushroom cap" over the large vent opening to keep out leaves, squirrels,
birds, etc.

You may also want to check the float level in the toilet. It may be set
too low and not giving you the full 1.6 gallons with each flush. Or the
flapper may be closing too early, causing the same problem.

I've been looking at more expensive toilets which may help
reduce the chance of the toilet clogging

We bought inexpensive off-the-shelf American Standard toilets from Lowes
when we built our house 2 years ago. I made sure to pick models with a
large trap diameter, but otherwise we just chose a style we liked. We
haven't had a single clog in the year or so we've lived here, and they
flush better than the 3.5 gallon toilets we had in our last place.

Unless the toilet was one of the first 1.6 gallon models that came out, I
wouldn't worry much about the toilet. If you would feel better replacing
it, I'd just pick up a new toilet, and not worry about all the pressure
assist stuff. They'll just cost more and be a future maintenance issue...

Anthony