Does the length of a p trap affect flow rate?

[Ian Simpson]

This is my first plumbing project and I’m not sure what’s going wrong. I had to make an extended p trap to go under some water supply lines but now that I’ve got it all together it seems to be draining way to slow. Could the length of the p trap be causing the slow drain rate? I did a bunch a research and couldn’t find anything that said this wouldn’t work. Any other reasons why this would be draining slow? See the attached images.

 

[Terry]

The copper pipes should have been moved around the drain. I have never done a shower that way. Waste and vents go in first, and water goes in around that.
Also, ABS doesn't glue to PVC

 

[Sponsor]

 

[Ian Simpson]

The copper pipes should have been moved around the drain. I have never done a shower that way. Waste and vents go in first, and water goes in around that.
Also, ABS doesn't glue to PVC

Hi Terry, those copper pipes were already there when I opened the floor and I don’t currently have the tools to change them. The vent is about 5ft away and the main sewer line is 4ft from that. Do you think that the length of the p trap is the issue? I haven’t been able to get a straight answer from anyone. Or if you have any recommendations on how I could change the PVC to increase the drain rate? Thanks.

 

[wwhitney]

I have no idea whether an elongated p trap like that would work or not. But since it's very unusual, and since you are having trouble, eliminating it seems like the best place to start.

Get a new shower drain body with PVC tailpiece and a conventional PVC p-trap. I think the gap between the two side of the return bend of a 2" p-trap is at least 2". Depending on where those copper lines are secured, you may be able to move them a little or at least squeeze them together and secure them. Then they can pass through the U of the return bend. If that moves your shower drain a little, that's a compromise you'll have to make if you don't want to do any copper supply modifications.

Cheers, Wayne

 

[James Henry]

It's illegal. A trap is supposed to be self scouring.

 

[Terry]

Wow! That's a lot of water that just sits there. And a vent 90 at the bottom of the drain. That might be difficult to snake in the future.

You may notice that in the lower drawing I moved the water lines.

 

[Tuttles Revenge]

That amalgamation you built is Not going to work in the long term.. At least not for you.. it will put money in the pocket of the plumber who might come out to fix it later.

A ptrap is built a specific way for very specific reasons. The shape of it allows for the flow of the water to keep the trap physically clean of build up of debris. It holds the least amount of water that needs to be displaced the least distance. It allows for a mechanical snake to pass through safely and return without damage to both.

Either buy the tools to move the water lines and practice on some pipe and fittings first... then move the water lines around the properly installed trap and trap arm.. Or hire a plumber to come out and fix it now before you need to hire them to fix it later.

None of us can give you advice on how well that setup will work because NO PLUMBER ever installs anything like that.

Hope that was straight forward enuf.

 

[Ian Simpson]

Hey guys thanks for the advice so far. I took the advice and removed the amalgamation and tried to fit the supply lines around a p trap without success. So I cut a portion of the pipe out to add a little elbow to go around the p trap, however, it turned out to be a thick brass pipe. The pipe walls are too thick for shark bite. Has anyone found a way to connect 3/4” brass pipe to 3/4” PEX pipe?

 

[Terry]

Brass pipe like galvanized pipe? Not copper?
You can rent a pipe threader for that and put some threads on the ends and then use a female adapter to PEX fitting.
I helped out my son on a late night job in Seattle for one of his relatives and I wound up renting the pipe threader from Home Depot in the tool rental section. .
Pick up some oil for that too. They have that in the plumbing section.

 

[wwhitney]

An accurate measurement of the OD would help. 0.625" would be 5/8" CTS (copper tube size), 0.875" would be 3/4" CTS, 0.840" would be 1/2" Schedule 40, 1.05" would be 3/4" Schedule 40.

What do you mean by "the pipe walls are too thick for shark bite"? If the pipe is CTS, but the little plastic stiffener inside the sharkbite doesn't fit inside your pipe, just remove the plastic stiffener. That's only required for PEX and the like, not for copper.

If the pipe is Schedule 40 size, I think there may be push to fit potable water fittings for it, but it would take a bit more research, so I'll wait to hear back.

Cheers, Wayne

 

[Tuttles Revenge]

Or press on Stainless Viega adapters.

Viega MegaPress Stainless and ProPress Stainless pipe fittings are available in two lead-free grades: 304 and 316. The latter is engineered for potable water systems in commercial and industrial environments, with more than 200 configurations available in sizes ½" to 4". EPDM sealing elements are also used in this case to optimize performance.

 

[Plumber69]

I've had to do this with a sani plus system. No issue yet 3 years later

 

[DIYorBust]

If it's brass, the easiest way would be to unscrew the two closest joints if they are accessible. If you have to cut, sylvan has suggested brazing a TP adapter, but that would require some skill. Rethreading in place might be the best solution, but will probably end up being more difficult than it sounds. Another option could be to lower the drain but there is a joist in the way.