P-Trap Questions

kwright402

Member
Feb 19, 2021
11
Rockwall, TX
Like many other cities ours requires the installation of a p-trap on our sewer drain at the time the pool is built, even though we are using a cartridge filter. We won't have a drain line running from the pool equipment, just a spot that we can run a hose to when we need to pump water out of the pool. I will include a picture below. (In the pic the p-trap portion has been left uncovered until the city inspection.

I have a few questions about this:

1. Do folks tend to leave the tops of these uncovered when not in use? (I'm thinking about debris or critters that could end up in the pipe.)

2. I know the purpose of the p-trap is to prevent sewage fumes from wafting out of the pipe. However, if the pipe is rarely used any water at the bottom of the p-trap will evaporate and we will have sewage fumes in the front yard unless we replenish the water at the bottom of the trap. Do I need to periodically put a little water down the pipe to take care of this?

3. I'm leaning toward putting a cap on this pipe and sealing it when not in use. Any reason not to do this?


ptrap.JPG
 
Get a bigger cap like a mushroom. Drill pilot holes in the cap and Use three 3.5 inch coated deck screws through the cap to hold it to the pipe. Plenty of air will get in but it will limit the evaporation and keep critters out.
 
Haha nice!
I did exactly that for an old water heater roof vent, no longer needed. (Replaced w a tankless water heater.
The mushroom cap I got from Lowe's. Home Depot didn't have anything like that. I suspect it's big enough for that p trap pipe too.
 
  • Like
Reactions: Newdude
The mushroom cap I got from Lowe's. Home Depot didn't have anything like that. I suspect it's big enough for that p trap pipe too.
They make caps in every pvc size to 6 inches at the home centers and hardware stores. One inch larger is probably plenty but 2 would work as well. Probably hit/miss these days as to who has stock tho. Google any plumbing supply shops by you. They’ll have the best selection.
 
Just cap it off when not in use. As you said, you are rarely going to use it. When you open it up to use it eventually you might get some sewer fumes but the water will take care of that. No need to over-think it.
 
  • Like
Reactions: borjis
Fill the trap with mineral oil if you are not using it for a long period. The oil will not evaporate. If you need to use it, pump your water down there and refill with mineral oil.

--Jeff
 
  • Like
Reactions: JoyfulNoise
Why wouldn't you plumb it in with a valve in case you have to lower the pool level? I have a cart filter, but have had to lower my pool water several times this year after heavy rains.
 
Why wouldn't you plumb it in with a valve in case you have to lower the pool level? I have a cart filter, but have had to lower my pool water several times this year after heavy rains.

Local building codes vary a lot on this issue but many do not allow a direct, hard pipe connection to a sanitary sewer as a pool pump can easily overwhelm the max flow rate limitations causing a backup into the home or damage to a municipal line. Many municipalities also require that pool water discharge into a sewer is free of any filtering media (like DE) and that the FC levels are below 0.5ppm or less. Someone could accidentally screw up their pool water by adding to much chlorine or making it too acidic and then decide to drain that into a sewer where it could potentially cause damage.

But, from a practical standpoint, given all the critters that can crawl back up a sewer line and the possibility of sewer gas (methane) coming back out, I would always opt to keep it as temporary connection and just cap off the sewer. If a person lives in an area with significant rainfall, then the pool should be designed with wall drains to manage overflow.
 

Enjoying this content?

Support TFP with a donation.

Give Support
Like many other cities ours requires the installation of a p-trap on our sewer drain at the time the pool is built, even though we are using a cartridge filter. We won't have a drain line running from the pool equipment, just a spot that we can run a hose to when we need to pump water out of the pool.
I was going based on the start of the thread... Sounds like the city required a p-trap for pumping water out of the pool. The pool pump overwhelming the max flow rate does make sense.
 
Thread Status
Hello , This thread has been inactive for over 60 days. New postings here are unlikely to be seen or responded to by other members. For better visibility, consider Starting A New Thread.