can I use a toilet drain as a sink drain?

8475 Views 20 Replies 10 Participants Last post by jeffnc, Mar 3, 2021

DanDaMan

Discussion Starter · Feb 9, 2020

We made a reno in our basement. The basement originally had 2 bathrooms, but since only 1 is needed (and typical), I gutted the one bathroom and we are converting it into a mudroom. I already removed the vanity and toilet, and temporarily put a plug on the toilet drain. Where the toilet originally was is where we want a small laundry style vanity and sink - I already ran a hot water line to this area, and obviously already have the cold water (from the old toilet). My question is whether I can use the toilet drain for my new sink drain? Is there a common adapter at hardware stores for this (ie. some type of 4" plug that has the typical 2" adapter for a sink drain? Also, should I be concerned about smell, or back pressure up into the sink? Lastly, would I just plumb it all up, or will I need one of those separate pressure valves on the sink line (to help it drain down).

Thanks

1 - 20 of 21 Posts

Missouri Bound

· #2 · Feb 10, 2020

As far as any sewer smell or back pressure that won't be an issue.
Your sink trap will take care of any sewer gas and there should be no back pressure.

I do not see any problem with your idea.
But I am an amateur plumber at best.
Perhaps someone more qualified can respond.

TheEplumber

· #3 · Feb 10, 2020

You can remove the flange, bush the toilet line down to a 2" line. Then plumb it as a normal sink. This would include adding a vent and P trap. You might be able to add an air admittance valve if your code folks allow them.

Reactions: 4

MTdiy

· #4 · Feb 10, 2020

I work for a plumbing wholesaler so I know a tinybit. I don't feel that this is an issue but yes you will need to adapt. I'm trying to imagine what you have going on here so bear with me. What kind of material is your toilet drain into the ground? PVC or cast iron? If it's PVC, they make what's called a bushing that is basically a donut with 4" 'outside diameter' and 2" inside diameter. I don't think pressure should be an issue either & if you're worried about smell, I would add a p-trap on your vanity.

DanDaMan

Discussion Starter · #5 · Feb 10, 2020

TheEplumber said:
You might be able to add an air admittance valve if your code folks allow them.

I'm an amateur. If I don't vent it and don't add a air valve, what would the result be? Would it basically drain slow and gurgle when it drains? Any idea how to find out if Calgary (Alberta Canada) code allows the air admittance valves?

Also, instead of busting up the floor and existing 4" toilet drain, I'm just wanting to put some type of adapter on it to convert it to a 2" sink drain line. Is this available at hardware stores? Looks don't matter since I will be putting in a cabinet style vanity and sink, so the plumbing will be hidden. Though at the same time I don't want to do something that is against code or obviously wrong, since it will be visible if the drawer is opened and I don't want potential issues one day when I sell.

Thanks

Missouri Bound

· #6 · Feb 10, 2020

TheEplumber said:
You might be able to add an air admittance valve if your code folks allow them.

As a vent?
Since the toilet was already plumbed, wouldn't there be a vent in place already?

Reactions: 2

DanDaMan

Discussion Starter · #7 · Feb 10, 2020

Missouri Bound said:
As a vent?
Since the toilet was already plumbed, wouldn't there be a vent in place already?

Dumb question - how would I know - what does a vent on a toilet drain look like? The mudroom is above my 4' crawl space, so I have easy access under the toilet (now sink) - if I recall the 4" toilet drain tied into many other toilet drains (I have 6 toilets in the house) and eventually out. Obviously the toilets are vented somewhere.

So, sounds like I don't need any vent or air admittance valve. Just get a 4" to 2" adapter, plumb up the sink, and voila.

BTW - is there any code against having a sink drain on the floor? All other sink drains I ever seen have the drain going into a wall. I don't think it is an issue, but just asking.

Thanks

Missouri Bound

· #8 · Feb 10, 2020

DanDaMan said:
Dumb question - how would I know

Thanks

I really wasn't asking you.

TheEPlumber was commenting on the vent situation.
When toilets are initially plumbed they are usually vented through the main stack
I was wondering why he would think otherwise.

TheEplumber

· #9 · Feb 10, 2020

2

Missouri Bound said:
As a vent?
Since the toilet was already plumbed, wouldn't there be a vent in place already?

Yes, a toilet drain will have a vent. But, a vent needs to be above the weir of the trap (except for toilets as they are self syphoning traps). With a toilet, the vent connection point will be downstream, underslab. Not in the wall where the sink P trap will join the drain.

See less See more

Reactions: 1

Missouri Bound

· #10 · Feb 10, 2020

Got it, thanks.

TheEplumber

· #11 · Feb 10, 2020

Toilets are sometimes vented on the main stack. But, if his toilet is actually vented as the image I posted shows, the it would probably be acceptable to connect the sink drain to the toilet vent and use it as the the drain and vent. This would be a typical wet vent. Something like this might work-

See less See more

DanDaMan

Discussion Starter · #12 · Feb 10, 2020

TheEplumber said:
Toilets are sometimes vented on the main stack. But, if his toilet is actually vented as the image I posted shows, the it would probably be acceptable to connect the sink drain to the toilet vent and use it as the the drain and vent. This would be a typical wet vent. Something like this might work-

So my question. Can I connect a sink directly to the toilet floor drain in your picture? I removed the toilet, and it is in that area where I want a sink now. I already ran a hot water line to that area, and have the cold water line (from the old toilet). Can I simply buy a 4" to 2" adapter, silicone it into the toilet floor drain, and then connect my sink to it?

Thanks

TheEplumber

· #13 · Feb 10, 2020

Not knowing exactly how your plumbing is done, this is my best answer-

TheEplumber said:
You can remove the flange, bush the toilet line down to a 2" line. Then plumb it as a normal sink. This would include adding a vent and P trap. You might be able to add an air admittance valve if your code folks allow them.

Old Thomas

· #14 · Feb 10, 2020

If you don’t have a vent as shown above the trap seal you will need a p trap, which is not allowed, and it could siphon out and stink. An air admittance valve will suffice.

Ghostmaker

· #15 · Feb 10, 2020

Just a stupid question but why don't you just reuse your old sink drain?

DanDaMan

Discussion Starter · #16 · Feb 12, 2020

Ghostmaker said:
Just a stupid question but why don't you just reuse your old sink drain?

Because I had a partition wall where the old vanity was - I knocked out this wall. So basically the old drain was plugged at the floor and I then covered it with tiles. Plus where this sink was is on the opposite side where the toilet was, so if I were to use it I'd have to run ~10' of extension to get the drain to where I now want the new sink. Being the area of the new sink was a toilet, I simply want to use that toilet drain for my new sink

Missouri Bound

· #17 · Feb 12, 2020

Here's what I would do, based on all of the recommendations and advice here.
I'll assume you are putting the sink against a wall.
Plumb the drain with a tee and plug it. Run the drain into the floor drain as planned. If you need to add an AAV you will have the tee there to do so.
It is unlikely you will need one since the overflow of a vanity sink will provide air.
And the toilet pipe already installed has a vent already.

ReidJustin

· #18 · Mar 3, 2021

We wanted to convert the bathroom into a toilet room,is it even possible to do this without getting an unpleasant smell?

AveryMolly

· #19 · Mar 3, 2021

Well, what I can tell you is the best way to see this in practice, of course, it is not advisable to redo the purpose of the rooms because there were previously brought sewer pipes of a certain structure and this can affect the effectiveness of the devices. We also redid the room and wanted to make a toilet room, put the toilet and noticed that there was a very bad smell from the sewer, it's all because of the structure of the pipes. We solved this problem by buying a toilet bowl on the advice of this site strongest flushing toilets with a check valve that delays unpleasant odors, this does not affect the functionality.

Ciceniss

· #20 · Mar 3, 2021

AveryMolly said:
Well, what I can tell you is the best way to see this in practice, of course, it is not advisable to redo the purpose of the rooms because there were previously brought sewer pipes of a certain structure and this can affect the effectiveness of the devices. We also redid the room and wanted to make a toilet room, put the toilet and noticed that there was a very bad smell from the sewer, it's all because of the structure of the pipes. We solved this problem by buying a toilet bowl on the advice of this site strongest flushing toilets with a check valve that delays unpleasant odors, this does not affect the functionality.

Thank you so much for your advice my husband and I are already going to buy a toilet on your advice, we found a model from a quality company ceresit. We really hope that there will be no problems with unpleasant odors, and we are already ready to do a full repair of the new toilet room. Thanks for the help

1 - 20 of 21 Posts

This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.