That comment from my plumber about drain slope changed my whole approach

I was redoing my shower drain and a plumber buddy stopped by, said my 1/4 inch per foot slope looked fine but he always goes with 3/8 inch for showers because of soap scum buildup. Switched it out on that job and haven't had a slow drain complaint since. Anybody else get specific pipe advice that made you rethink standard codes?

4 comments

4 Comments

sean_barnes2417d agoMost Upvoted

Man, that's a REALLY good point about soap scum! I always thought the standard 1/4 inch was the magic number but your buddy's logic makes TOTAL sense for showers where soap buildup is constant. So did you actually have to rework the whole drain pipe to get that extra 1/8 inch, or was it just a matter of adjusting the hanger brackets a bit? I'm wondering if going steeper ever causes issues with water just rushing past the trap or something weird like that.

phoenix_grant17d ago

So you're wondering if a steeper pitch can mess with the trap seal? I've actually seen that happen a couple times when guys get too aggressive with the slope. Water can blow right past the trap if it's too steep, and then you get sewer gas in the house. But for a shower, going from 1/4 inch to 3/8 inch per foot is usually fine. The real trick is making sure the pipe stays smooth so soap scum doesn't grab on.

williamw7517d ago

Wait, did you check what happens with the venting when you go steeper? I had a buddy who did that same 3/8 slope on his shower and ended up with this weird gurgling sound every time the toilet flushed upstairs. Turns out the steeper drop was pulling water out of the trap a little bit and it was barely hanging on. He had to add like a little Studor vent under the sink just to keep the air balanced. Funny thing is the shower itself drained great, no soap scum at all, but the whole system acted funny for a week before he figured it out.

ray_sullivan17d ago

Yeah I remember reading something about this in a plumbing forum a while back, a guy was saying how steeper slopes can actually cause the water to run so fast it aerates the waste and the solids don't get carried as well. But for showers it's different because it's mostly liquid and soap residue, not solids. I think the key is keeping the pipe clean and smooth, like your buddy said about the soap scum. Also, I heard that the shallower the slope the more chance of stuff settling and causing clogs, so the extra 1/8 inch might be the sweet spot for that kind of buildup. I've never had to mess with the trap seal issue myself, but it makes sense that too steep could blow past it, like a water slide. Seems like a tradeoff between flow speed and letting the trap do its job.