Ask Me Help Desk - Toilet drain questions

We're installing a new bathroom on the third floor of our old house. The toilet is on the wall opposite the 3” stack. The 3” drainpipe from the toilet will run horizontally about 8 feet to where it will pick up the 2” lavatory drain (vented) in a 3x3x2 wye. The 3” drain will then turn and drop about 2 feet and enter the stack in a 3x3x3 wye. I have two questions.

1) The floor joists are truly 7”x2” (an old house). If we install the closet bend so the top is level with the floor, there will be just over 1/8th inch drop per foot for the horizontal portion of the drain. While this slope is apparently marginally acceptable, I would like to know if we could trim the top of the closet bend (and the bottom of the toilet flange) to raise the bottom of the closet bend and, thereby, increase the drain slope. In other words, can we get away with less than the 1.5” overlap for the PVC weld?

2) I believe the 3” drain is properly vented by the above arrangement. However, I could also vent the drain to the wall behind the toilet by inserting a 3x3x2 wye at about a 45 degree angle just after the closet bend, running the 2” pipe for about 18” with an upslope of at least ¼” inch per foot before the vent would turn vertical. This arrangement would allow me to put a cleanout on the vent line from where I could snake out almost all of the 3” line. Is this a good idea?

Thanks in advance for your help.

1) "The floor joists are truly 7”x2” (an old house). If we install the closet bend so the top is level with the floor, there will be just over 1/8th inch drop per foot for the horizontal portion of the drain. While this slope is apparently marginally acceptable, I would like to know if we could trim the top of the closet bend (and the bottom of the toilet flange) to raise the bottom of the closet bend and, thereby, increase the drain slope. In other words, can we get away with less than the 1.5” overlap for the PVC weld?"

While 1/4" to the foot is normal it's not set in stone. !/8th is acceptable if slope's tight. We put in lots of new installations at 1/8th to the foot. In case you're wondering, 1/8th is just cracking the bubble on your level.

2) "I believe the 3” drain is properly vented by the above arrangement. However, I could also vent the drain to the wall behind the toilet by inserting a 3x3x2 wye at about a 45 degree angle just after the closet bend, running the 2” pipe for about 18” with an upslope of at least ¼” inch per foot before the vent would turn vertical. This arrangement would allow me to put a cleanout on the vent line from where I could snake out almost all of the 3” line. Is this a good idea?"

Cleanouts are always a good idea. Especially if the homeowner is a do-it-yourselfer. Your toilet will be vented by the lavatory in any case. I don't see a tub or shower. Is all you're planning a 1/2 bath? Regards, Tom

Tom - Thank you for your help.

The shower drain will run in a parallel joist space, turn down in a long sweep, and join the toilet line in a 3x3x2 wye immediately before the toilet line enters the stack. The shower will be vented to the opposite wall in a similar way as I proposed for the toilet, allowing a cleanout for the shower line as well.

Quote:

Originally Posted by dclynch

Tom - Thank you for your help.

The shower drain will run in a parallel joist space, turn down in a long sweep, and join the toilet line in a 3x3x2 wye immediately before the toilet line enters the stack. The shower will be vented to the opposite wall in a similar way as I proposed for the toilet, allowing a cleanout for the shower line as well.

Sounds good to me. Cheers Tom