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Plumbing in the Home/Bath drain line configuration


Future Basement Bath Area
Future Basement Bath A  
QUESTION: Hi Thomas:

Check out the attached picture. This future basement bathroom was plumbed for a sink and toilet but not for a shower (which is now in the plans). The shower will be situated to the far right of the picture on a base to allow for the trap and with the vanity between the shower and the toilet. My question is (without knowing the exact distance): does it appear that I will have enough pitch to wrap around that wall and connect to the drain pipe (shown)? Also, do I need to make a drain run all the way or can I relay to the sink drain and then out to the plumbed drain? Thanks in advance.

ANSWER: Dear Kevin,

   The required pitch for a drain line is 1/4" per foot (horizontal).  So, if the total length of pipe from the shower trap to the drain in the floor was 4 feet... then it would have to drop 1".

   I would measure the distance that the pipe will need to run along the wall and around the corner... then calculate the rise using .25 times the number of feet.  Then place a tee fitting of the proper size on the floor so that you can determine the lowest point of the shower drain line.  Once you have that lowest point and the total rise you can determine the height that your platform will need to be.

   When I have had to set showers in similar circumstances I would break the floor around the pipe enough to set my tee or wye fitting so that I could get a little bit of extra depth, it's a simple thing to patch the concrete.

   The problem of connecting to the sink drain as I believe you were thinking is that the sink drain will be considerably higher than the shower.

   Another thing to consider before finishing this project is the venting.  Each trap (for the sink and the shower) needs to have a vent within a few feet.  Without proper venting the traps can siphon and allow gasses and odors escape.  Unless you have a vent from the upstairs plumbing conveniently close by you might want to use a mechanical vent for those two fixtures.

---------- FOLLOW-UP ----------

QUESTION: Thanks for your help Thomas. Your explanation clears a lot of things up. In terms of the venting, notice the picture I sent this time. That capped pipe is part of the vent system and it lines up perfectly with the floor drain. All I need to do is run PVC up and over to tie in. My followup question is, would the sink drain tie into the floor drain with its own tee at a point right above the shower tee? Thanks in advance.

Yes Kevin, I would place a tee at the lowest possible point for the shower drain and the tee for the sink somewhat above that... you will want to keep the pitch in mind for the sink as well because too much pitch can cause problems too.

Also if you plan to frame out the bathroom you should do the framing first and run the pipes through and around the structure.

The sink drain can be 1.25" pipe, but the shower should be 1.5" at least... 2" would be required for a bathtub.  

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Thomas Ambler


I am experienced at troubleshooting and solving all types of plumbing problems. Issues related to specific manufacturers fixtures and specifications though are beyond my field of expertise. I have dealt with problems in both rural and urban areas, and with water supply and drainage systems. Plumbing issues can be very obscure... such as odors, stains or occasional seepage. I have even had to chase rats from a customer's sewer line.


I have 25 years experience dealing with plumbing systems (which also includes hot water and steam heating systems). My main expertise is in diagnosing and solving problems. I have worked in construction and installation of new systems but do not regard myself as an expert in that area.

Asbury Park Press, Seattle Times, Denver Post.

I completed high school and one year of college. I served 4 years in the Marine Corps and have education in electronic and electrical troubleshooting and repair. I have attended classes on installing and repair of oil burners, and I have EPA universal certification for air conditioning and refrigeration. I am now enrolled as a full-time student at Everest college to re-train for a new career. Any donations of financial support would be greatly appreciated.

Past/Present Clients
All of Denny's Restaurants in NJ, Several Burger King stores, I have done work at two different homes for Bruce Springsteen. I have also worked for Jim Johnson (of J&J) and his family, Whitney Houston, Steve Forbes and many others.

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