Replacing Bathtub S-Trap with P-Trap

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Munnik

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Wife wants a soaker tub so here I am. The new tub drain lines up with the existing drain horizontally but is 6 inches further away from the wet wall. The current tub was installed many years ago and when I climbed under the crawl space to look over the plumbing, I found it was connected to the 3 inch drain line with an S-Trap. While this never presented a problem with the current tub, I know this is not optimal. Because the drain needs to be moved, if possible I'd like to replace the S-Trap with a P-Trap.

The existing tub with S-Trap is connected to the 3 inch drain line. I plan to replace the S-Trap with a P-Trap and connect it to the existing 2" vent stack. Currently the shower is connected to the 2" vent stack and would need to be moved down to the stack to make room for the tub drain.

I plan to get a permit and was told by the County to call MDIA and talk to an inspector to see exactly what permit would be require. I found out the inspector for my area is has stopped doing inspections of occupied homes because of the pandemic. I hoping he will be open to reviewing proposed changes electronically.

The attached picture is the proposed plumbing changes. Note there is plenty of space for maintaining the correct slope in the drain lines. Any constructive comments are appreciated and welcomed.
 

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Munnik

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It looks good to me. You have studied well.

Thanks so much for the timely response. Have to give the wife credit for the studying. She got on-line and found your site and the reference to the helpful hints and some training material from another site. Used what she studied to draw the above plumbing diagram. She has some hesitation about her interpretation of the material and asked me to post her diagram on your site. She's very happy to hear your response. She asked me to share the links. Great information.


https://www.co.lincoln.or.us/sites/..._-_helpful_hints_residential_construction.pdf

http://www.plumbingpros.com/pdf/dwvents.pdf
 

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Follow on question. Due to space constraints, it is too difficult to stack 2 fittings for the bath and shower on the vent pipe. I initially proposed using a 2" x 2" x 1 1/2" x 1 1/2" double san tee. As noted by my astute wife, our new TOTO toilet came with installation notes for back to back toilet install which recommends double wye in place of a double san tee. Is this applicable to our situation and what appears to be a back to back tub/shower install (see attached picture)?
 

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Terry

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A toilet bowl is designed to siphon and then be refilled with water from the tank.
A shower or tub is not meant to siphon and in fact the vent is there to prevent siphoning. A double wye does not work for a shower or tub, nor does a wye a combo for a single tub or shower. A double fixture fitting may be used. I would pick up a 2" double fixture and bush down for the tub trap arm to 1.5" leaving the three other sides at 2".
 

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A toilet bowl is designed to siphon and then be refilled with water from the tank.
A shower or tub is not meant to siphon and in fact the vent is there to prevent siphoning. A double wye does not work for a shower or tub, nor does a wye a combo for a single tub or shower. A double fixture fitting may be used. I would pick up a 2" double fixture and bush down for the tub trap arm to 1.5" leaving the three other sides at 2".

Terry... thanks so much for getting back to me so quickly. I was hoping for your suggestion with a small exception. The vent pipe is 2 in the shower and the tub trap arms are 1 1/2 in. I found a 2-in x 2-in x 1-1/2-in x 1-1/2-in Double Sanitary Tee Fitting at our local big box store (see picture). Is there any reason this will not work place of your recommended 2" double fixture and bush down for trap arms.
 

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Terry

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It would be very difficult to ever snake that fitting. Tubs wind up with a lot of hair down the drains.

double-fixture-tee.jpg


photo taken at a Home Depot
 

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So I am confused but the fog is lifting. The material we read indicated that p-traps should be connected using san tees and not combo wyes as you reinforced with your response. The fitting above quite different than the double san tees sold at lowes. I can see how it would allow for easier snake. I may have a problem finding the PVC version at Lowes. I assume it comes in PVC too. May have to special order that one. Thanks again.
 

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hj... you are right. That was the original drawing. Stacking would give me the flexibility of positioning the trap arms so that I would have a straight shot to the shower and tub without using any bends. But the space just doesn't allow it. Maybe the wife's original approach is best.

Question with the original approach, would it be necessary to use a combo wye or would a san tee work in that location. It would not be in a horizontal position like the existing 3x3x2 combo wye.
 

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Sorry if I confused you. Hope this not so good sketch explains what I am asking.
 

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Munnik

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Sorry if I confused you. Hope this not so good sketch explains what I am asking.

Never mind... we answered our own question. After finding the attached illustration in another thread, it is clear why a san tee will not work at the bottom of the vent stack/ wet vent. Even though the flow from the tub is vertical, the flow from the sink is horizontal which will result in waste backflow if a san tee is used. So we have our material list and as long as our space the dimensions of the fittings allow, we have our final design.

Sorry for beating the wye or wye not dead horse. Thanks all for the input and your review of our posts.

index.php
 

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