Master Bath plumbing - slope and vent lines

[Mark R]

I recently remodeled our Master Bath and replaced both the tub and shower. The drain plumbing didn't change except for adding new P-traps. Sometimes, there is an odor after using the tub or shower. My assumption is that the slope isn't correct and that the water is getting pulled out of the trap. Attached is a very crude drawing of our setup.
Can someone educate me a bit on the correct slope for the drain pipes and how I should troubleshoot this issue?

 

[wwhitney]

Two questions:

What's coming in on the horizontal line that's open on the left?

And is your drawing a perspective, showing that the lines from the p-traps to the horizontal line are horizontal at a right angle, or is it an elevation, showing that those lines are sloped downward a fair amount?

Cheers, Wayne

 

[Sponsor]

 

[Jeff H Young]

1/4 inch per foot slope . looks to be improperly vented the tub and shower on same trap arm could be improperly depicted by drawing though

 

[Mark R]

I think the sinks are connected to this line also, but I would have to double check.

The drawing is not to scale, so the pipes have some slope, but not as much as shown

Two questions:

What's coming in on the horizontal line that's open on the left?

And is your drawing a perspective, showing that the lines from the p-traps to the horizontal line are horizontal at a right angle, or is it an elevation, showing that those lines are sloped downward a fair amount?

Cheers, Wayne

 

[wwhitney]

If the sinks are coming in from the link, and are the only fixtures coming in from the left, then your tub and shower could be properly wet vented. For the tub and the shower, the trap arm starts at the trap outlet and extends to the connection to the horizontal line at the bottom of the drawing. Each trap arm needs to have a fall of no more than 1 pipe diameter over its length (while still being sloped at least 1/4" per foot). If the trap arm fall is greater than one pipe diameter, that could cause siphoning of the trap, which could cause bad smells.

If the smell is repeatable and persists, rather than being intermittent, you can check if trap siphoning is the problem. When you notice the smell, pour around a quart of water into the drain. If that stops the smell, then the trap was empty.

Cheers, Wayne

 

[Jeff H Young]

can't really trust drawing but looks to be plumbed wrong

 

[Reach4]

I think the sinks are connected to this line also, but I would have to double check.

The sinks as in laundry or kitchen sinks, or sinks as in lavatories (bathroom sinks)? It matters.

 

[Mark R]

The sinks as in laundry or kitchen sinks, or sinks as in lavatories (bathroom sinks)? It matters.

Bathroom sinks

 

[Mark R]

The > 1/4" slope should be maintained all the way to the vent, correct?

If the sinks are coming in from the link, and are the only fixtures coming in from the left, then your tub and shower could be properly wet vented. For the tub and the shower, the trap arm starts at the trap outlet and extends to the connection to the horizontal line at the bottom of the drawing. Each trap arm needs to have a fall of no more than 1 pipe diameter over its length (while still being sloped at least 1/4" per foot). If the trap arm fall is greater than one pipe diameter, that could cause siphoning of the trap, which could cause bad smells.

If the smell is repeatable and persists, rather than being intermittent, you can check if trap siphoning is the problem. When you notice the smell, pour around a quart of water into the drain. If that stops the smell, then the trap was empty.

Cheers, Wayne

 

[wwhitney]

I don't really follow the question. All horizontal drains have to be sloped at least 1/4" per foot, unless they are large enough to be sloped at 1/8" per foot. The IPC allows 1/8" per foot for 3" lines, but my understanding is that when you have available fall, 1/4" per foot is still better. And any horizontal vent sections should similarly be sloped back towards a drain at 1/4" per foot, so they will empty if they ever temporarily fill during a backup (or during initial testing).

The point about the trap arm is that there is both a minimum rate of fall, and a maximum total fall; hence a maximum length, which is achievable only when the actual rate of fall matches the minimum.

Cheers, Wayne

 

[Mark R]

Thank you for your help and trying to educate me.
Here is a picture showing the shower trap arm. The trap is just out of sight to the left. I have corrected the slope on the shower drain (the slope was too shallow). What about the wye connection at the far right? Is this OK? The vent would be at the end of this second horizontal drain pipe (at the far left of the picture). The second drain line seems to be sloped correctly.

I don't really follow the question. All horizontal drains have to be sloped at least 1/4" per foot, unless they are large enough to be sloped at 1/8" per foot. The IPC allows 1/8" per foot for 3" lines, but my understanding is that when you have available fall, 1/4" per foot is still better. And any horizontal vent sections should similarly be sloped back towards a drain at 1/4" per foot, so they will empty if they ever temporarily fill during a backup (or during initial testing).

The point about the trap arm is that there is both a minimum rate of fall, and a maximum total fall; hence a maximum length, which is achievable only when the actual rate of fall matches the minimum.

Cheers, Wayne

 

[Jeff H Young]

need a vent on that shower

 

[Mark R]

Please elaborate…