Hello Experts,

My son and I are doing the new DWV system for our house. I have a lot of experience in doing plumbing so I'm not a novice, but I do need to make sure I am doing the venting properly (I know the vent is just as important as the drain lines) as I haven't done anything quite this complex.

There is a main 4" drain line in the middle of the house that splits to 2 3" lines, one going to the master bath and a half bath, and the other going to the other end of the house that has 2 back-back bathrooms (mirror images of each other). The kitchen sink and island sink dump straight into the main 4" line; these 2 drain lines vary from 16" to 24" below the subfloor.

As you go upstream to the 2 bathrooms, there is a 3/3/1.5/1.5" double wye with street 45's that gets the drains from each tub/shower. The next thing the 3" line picks up is one toilet with 3" wye. The other toilet drops straight into the top of the 3" main line with a 3" tee-wye upstream from the other toilet. These 3 branches are within 3' of each other on the main 3" line. The last thing that dumps into the line is the drains for the 2 lavs. They are connected into a 2/2/1.5/1.5" double tee in the wall with the 2" drain running into the end of the 3" line; this is about 3' from the toilets. The lavs are obviously vented (which is correct, 1.5" or 2" for the lavs?) and I planned on running an 1.5" vent off of one of the tub/shower drains. Is this correct?

As you go upstream to the half bath and master bath, the first thing you come to is the toilet for the half bath. It has a 3" wye over to the toilet about 5'. The next thing that you come to (about 1' up the line) is a 3/3/1.5" tee-wye that goes to the lav in the half bath; this has 1.5" tee in the wall. Another foot up the line is a 3" tee-wye for the toilet in the master bath; it goes about 18" on the right side of the line to catch the vertical toilet pipe. The next fitting about 18" up the line is a 3/3/2 tee-wye going to the left about 2' for the corner shower. This then reduces down to 2" pipe. Next about 6-7' up the line is a 2/2/1.5" tee-wye for the drain of the corner whirlpool tub. I was planning on putting an 1.5" vent in the tub drain line. And lastly, the 2" line elbows over about 8' and up in the wall for the double vanity with a 2" tee (1.5" or 2" vent here?). Is this correct?

Also, one more thing, what is the proper way to vent an island sink (it is about 7' away from the main kitchen sink)?

I think that about takes care of it. Forgive me if I left important info out or wrote it confusingly. If something is missing that you need to know about, I'll gladly tell you what you need to know. Thanks for the help. I really appreciate it.

Hello Experts,

My son and I are doing the new DWV system for our house. I have a lot of experience in doing plumbing so I'm not a novice, but I do need to make sure I am doing the venting properly (I know the vent is just as important as the drain lines) as I haven't done anything quite this complex.

There is a main 4" drain line in the middle of the house that splits to 2 3" lines, one going to the master bath and a half bath, and the other going to the other end of the house that has 2 back-back bathrooms (mirror images of each other). The kitchen sink and island sink dump straight into the main 4" line; these 2 drain lines vary from 16" to 24" below the subfloor.

As you go upstream to the 2 bathrooms, there is a 3/3/1.5/1.5" double wye with street 45's that gets the drains from each tub/shower. The next thing the 3" line picks up is one toilet with 3" wye. The other toilet drops straight into the top of the 3" main line with a 3" tee-wye upstream from the other toilet. These 3 branches are within 3' of each other on the main 3" line. The last thing that dumps into the line is the drains for the 2 lavs. They are connected into a 2/2/1.5/1.5" double tee in the wall with the 2" drain running into the end of the 3" line; this is about 3' from the toilets. The lavs are obviously vented (which is correct, 1.5" or 2" for the lavs?) and I planned on running an 1.5" vent off of one of the tub/shower drains. Is this correct?

As you go upstream to the half bath and master bath, the first thing you come to is the toilet for the half bath. It has a 3" wye over to the toilet about 5'. The next thing that you come to (about 1' up the line) is a 3/3/1.5" tee-wye that goes to the lav in the half bath; this has 1.5" tee in the wall. Another foot up the line is a 3" tee-wye for the toilet in the master bath; it goes about 18" on the right side of the line to catch the vertical toilet pipe. The next fitting about 18" up the line is a 3/3/2 tee-wye going to the left about 2' for the corner shower. This then reduces down to 2" pipe. Next about 6-7' up the line is a 2/2/1.5" tee-wye for the drain of the corner whirlpool tub. I was planning on putting an 1.5" vent in the tub drain line. And lastly, the 2" line elbows over about 8' and up in the wall for the double vanity with a 2" tee (1.5" or 2" vent here?). Is this correct?

Also, one more thing, what is the proper way to vent an island sink (it is about 7' away from the main kitchen sink)?

I think that about takes care of it. Forgive me if I left important info out or wrote it confusingly. If something is missing that you need to know about, I'll gladly tell you what you need to know. Thanks for the help. I really appreciate it.
Good morning Dave,

We use 2" to vent our lavatorys but if space's tight 1 1/2" is acceptable. If you tie the tub drain into the lavatory drain you won't need a vent on the tub. It will be wet vented through the lavatory.
Is the upstairs shower vented or are you discharging a major fixture, the toilet , past a unvented minor one , the shower. Tie the shower line into the lavatory drain and wet vent it. The same for the whirlpool tub. While EVERY TRAP MUST BE VENTED, one vent per bathroom group is all that's needed.
As for the island sink. A circuit or loop vent is what you need to run . This consists of two lines under floor or ground running over from a vent stact and looping up to pick up the sink and then using a return bend above the tee to tie the two lines together. The lower line will be the drain and the upper one will be the vent. More questions? We're as close as a click. Cheers, tom

Thanks for the quick reply, Tom.

On the back to back bathrooms, the pair of lavs are at the end of the main 3" line, then downstream are the 2 toilets, and then the 2 tub/showers. Since this is 2 bathrooms, I just figured I would need 2 vents. Hence why I was figuring on putting a vent on one of the tub/showers. This wouldn't hurt anything would it?

On the master bath and half bath, they are also next to each other. With the half bath downstream from the master. Both toilets are discharging downstream from the shower, but the lav for the half bath is in between the 2 toilets and vented with 1.5" pipe. With space I have, I can't get the shower drain into the lav drain for the half bath; it has to go into the main 3" line. Since the whirlpool tub is discharged a few feet downstream from the double lav drain, I would assume that the whirlpool is vented through the double lavs, but not the shower? So what, if anything do I need to change around here?

Thanks for the quick reply, Tom.

On the back to back bathrooms, the pair of lavs are at the end of the main 3" line, then downstream are the 2 toilets, and then the 2 tub/showers. Since this is 2 bathrooms, I just figured I would need 2 vents. Hence why I was figuring on putting a vent on one of the tub/showers. This wouldn't hurt anything would it?

On the master bath and half bath, they are also next to each other. With the half bath downstream from the master. Both toilets are discharging downstream from the shower, but the lav for the half bath is in between the 2 toilets and vented with 1.5" pipe. With space I have, I can't get the shower drain into the lav drain for the half bath; it has to go into the main 3" line. Since the whirlpool tub is discharged a few feet downstream from the double lav drain, I would assume that the whirlpool is vented through the double lavs, but not the shower? So what, if anything do I need to change around here?

Sorry it took me so long Dave,


If the lavatory in the master bath is up stream from the toilets you may tie the shower in anywhere upstream from the two toilets and down strream from the lavatory and be wet vented. Have a great week end. Tom