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Bmbeeson 12-27-2007 09:25 AM

Basement Bathroom Rough-in questions
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First off, I have been lurking around here off and on for the past year and really love this site. Everybody here seems very helpful and forthcoming, that's awesome! Here's my situation:

I am currently in the mid-stage of finishing my basement and am ready to work on the bathroom plumbing. I am on a septic system and the house does not have a sump pit. I am very fortunate to have a super-dry basement!

I plan on installing a sink/vanity, toilet and, tub/shower combination. I snapped some pictures of what I currently have in the way of roughed in piping.

I have been told by a reputable local plumber that the toilet flange will have to be moved out from the wall a few inches to accommodate a toilet due to the fact that the original plumber put the pipe to close to the wall. He also told me that the shower/tub drain will have to be moved as well for the same reasons.

Here are my questions:

#1 - What is the "Mystery Pipe" (labeled "Not Sure") located to the left of the Shower Drain pipe? Is this an overflow drain for a tub?
#2 - How do I vent this bathroom?

Any help would be greatly appeciated, thanks!

Mike Swearingen 12-27-2007 10:45 AM

First, I'm not a pro plumber, just a long-time DIYer.
It appears to me that the "not sure" is an optional drain for a tub/shower unit, and the shower drain is for a "just a shower only" option. One or the other would remain capped off.
You've pegged the vanity sink and toilet drains.
The toilet drain should be centered usually at least 12" off of the finished wall (12.5" off framing with half-inch sheetrock to be added for instance). You may be breaking up concrete, replumbing a bit and re-cementing around the toilet if it isn't, or looking at a 10" center toilet, depending upon the distance now.
Remember that the flange itself should sit flush on top of the finished floor level with only the thickness of the flange itself above finished floor level. The flange should be bolted (Tapcons) to the concrete floor, and the toilet bolted to the flange, for the wax ring to seal properly.
If all of this rough-in plumbing passed inspection "back when", it all should already be vented properly. You just need to add the sink and shower traps and the toilet.
Good Luck!

beer_geek 12-27-2007 11:50 AM

Also not a pro. If you can ask the builder, it'd be better than guessing. First off, your "not sure" is quite possibly your vent. Again, not a pro, but, I've never seen a rough in for both a shower and tub in a room that can't hold them both. That's why I think it's the vent. What's in the ceiling? My builder roughed in the vent through the roof. However, it wasn't connected until I finished the bathroom. Lastly, what did your plumber say? Did he make a site inspection or just go by the pictures?

ranman469 12-27-2007 04:36 PM


its more than likely a vent. is there a PVC pipe roughed in above the bath location?
if not depending on your code of your state? it would be vented with AAV. air admittance valve. it lets air in no air or stink out.

Marlin 12-27-2007 06:53 PM

I can't read any of your labels but it appears that mystery pipe is a vent for your shower. You also appear to be roughed for a shower, not a tub. Tubs usually have a drain on either side, not in the middle unless you're going with a claw foot. If you are going with a shower their is no need to move this drain.

Their should also be a vent for the toilet waste. It may be wet vented through the sink drain (in this case the sink drain should be 2in, not 1-1/2.

How far out from the wall is the center of your toilet waste line? Their are toilets that require as little as 10" although your selection will be limited and they're mostly special order. Still cheaper then having a plumber chop the slab though.

Bmbeeson 12-28-2007 05:51 AM

Thanks for all of the reply's so far.

Mike/Marlin - My toilet drain is about 11 7/8" off of the wall. So it looks like I will either go with a 10" center toilet or it will be chop-chop city and relocate the drain. Thanks for the flange/toilet mounting info.

Geek - You are exactly right about guessing! Unfortunately I am not the original owner and I've been told through the grapevine that the original builder is no longer in the picture locally. Kind of stinks! After my plumber quoted the job I forgot to ask him some basic questions. I will give him a call and maybe even have him come back out to explain some things to me before I make a decision on how I will proceed.

DIY4EVER 12-28-2007 09:12 AM


I am not a plumber so I can not shed any light on your plumbing questions, however being a DIYer that just finished their basement project, I would take the time to put in a sump pit and pump. It sounds like you are already doing a bit of plumbing and taking the time to put the sump in now would be a good idea in my opinion.

I have a very dry basement and no plumbing in my finished basement but I did install a pump in my pit just to be on the safe side. I think it would be wise in your case since you are adding plumbing, even though your basement is dry. One burst pipe or one clog that causes a back up could be big $$$ in repairs.

just my two cents.

47_47 12-28-2007 10:56 AM

Instead of replumbing for the toilet drain, can you reframe the toilet into an alcove?

Ron The Plumber 12-28-2007 11:46 AM

That looks like the vent for the shower, and I'm a plumber.

Chris Johnson 12-28-2007 11:52 AM

Unlike Ron, I am not a plumber, what about an offset flange for the toilet? Requires minor chipping but should save a fair bit of $$$

JHill 12-28-2007 01:20 PM

I'm sorry to but in on your thread Bmbeeson but I'd like to see if someone can explain what exactly a "wet vent" is and the purpose of it.
I'm getting ready to finish off my basement bathroom as well and the wet vent is causing all sorts of confusion for me.

Thank you in advance.


Ron The Plumber 12-28-2007 01:25 PM

A wet vent is when a drain uses a separate fixtures vent to tie into, codes and restrictions can apply to the use of vent venting.

JHill 12-28-2007 01:32 PM


Originally Posted by Ron The Plumber (Post 83478)
A wet vent is when a drain uses a separate fixtures vent to tie into, codes and restrictions can apply to the use of vent venting.

When I hear vent, I think of air.

by vent you mean drain?

JHill 12-28-2007 01:54 PM

Nevermind........I found a diagram that explains my question pretty well.

Thanks Ron

Mike Swearingen 12-28-2007 05:05 PM

If my old buddy Ron calls your "not sure" a vent for the shower, then that is what it is. My "guess" missed it.
You'll have to break up some concrete and do some re-plumbing for anything but a shower there. An offset will work for the toilet. Check on the local code possiblities of Air Admittance Valves for the plumbing, if that rough-in isn't already vented.
Good Luck!

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