Kitchen Island plumbing.

[sa226]

I have a question regarding the drain for my kitchen island sink. We did some renos, which included replacing the island. Everything is in place now, I just need to figure out how to plumb the drain.

I was planning to just copy the old drain from the previous sink and island, but for whatever reason, in 1999 they figured that it was acceptable to put the P trap under the floor in the basement. I'd like to have better access to that trap once the basement is finished, so I would like to move the trap up to just below the sink.

The question revolves around making sure the drain is properly vented. I've been reading about island sink drain venting....loop vents, Air admittance valves etc. But the previous drain wasn't vented, so I'm confused.

Once the drain goes below the floor it runs about 8ft until it drops into a larger diameter "collector" pipe where the drains from the upstairs bathrooms and the downstairs half bath both drain into then it drains into the main stack. Presumably that whole deal is vented somewhere.

Can I just move the trap up from under the floor into the sink cabinet, let the trap run into a vertical drain with a cleanout then hook it up the the old drain line that runs the 8ft? Or do I need some fancy venting mechanism?

The internet tells me I need some fancy venting mechanism, but the previous drain didn't have one, so I'm confused.

Thanks.

[speede5]

No. If you move it up when you run water through it it will siphon and cause the trap to empty. The way it was done is fine, I am pretty sure you are supposed to be within 6 ft of the vent by code but if it was working before don't mess with it.

If you are in the floor replace the trap with 2" (assming it isn't already) and you will never have a problem.

If you insist on having the trap higher your only solution is a vent valve, unless you want a vent pipe coming up through your island. There are Vent valves that can pass but they are pricey and not available at most building stores. The cheater vents they sell are technically not up to code.

I should add I'm not a plumber, I've done lots of this type of work but always get a real plumbers advise on distances and diameters. Whatever you plan to do run it by a plumber to make sure your making it better not worse.

[Ducay]

Originally Posted by speede5

No. If you move it up when you run water through it it will siphon and cause the trap to empty. The way it was done is fine, I am pretty sure you are supposed to be within 6 ft of the vent by code but if it was working before don't mess with it.

If you are in the floor replace the trap with 2" (assming it isn't already) and you will never have a problem.

If you insist on having the trap higher your only solution is a vent valve, unless you want a vent pipe coming up through your island. There are Vent valves that can pass but they are pricey and not available at most building stores. The cheater vents they sell are technically not up to code.

I'm no expert, but I believe there are many admittance valves that are up to code, including many available at the box stores. Yes - there are the cheap $4 valves available that I'd never use but, there are good Oatey and other brands available that should meet the sizing and code requirements for a standard residential sink.

There are a few rise/run & trap things to consider when determining the drain & vent requirements, but with the limited info available (obviously specifics matter), I can't see why you couldn't raise the p-trap into the cabinet like most installs and also plumb in an admittance valve while you'reat in. Just ensure you're still meeting the requirements, but generally speaking, if you've got a good AAV and a consistent slope to the trunk line, should be fine.

Usually the tricker part is figuring out the trap location and rise to the main line when you are trying to position to avoid a required vent/or admittance valve, but if you can just as easy add one in, makes life easier.

[sa226]

Thanks guys.

So, given my situation, is the "accessible" trap and AAV the preferred method? Or just basically not messing with what worked before?

I'm just thinking down the road when the basement is finished, having to install little trap doors in the ceiling the be able to access the P trap.

The trap and drain are all 1.5 inch, which I guess would mean the run is 6ft ( 6, 1\4's?)

So if I'm understanding it correctly to prevent siphoning, you can't have anywhere downstream of the trap where the water "fills". If you have drain water crashing down like a waterslide into a 45 elbow or a sanitary T it will created a vacuum and siphon the trap. Whereas if its a nice slow trickle and 1/4inch per foot, air can still get back to the trap and its just gravity doing its thing?

[speede5]

Oh geez, I read "under the floor in the basement" and thought this a basement kitchen (suite). I was kinda wondering why there was no backflow prevention.

I wouldn't mess with what was there before if it worked. If you can bump up to 2" it's doubtful you would ever have a blockage where you need to access the trap, and could snake it easy enough.

You're understanding sounds about right.

[Rjcsjc62]

The "loop vent" as you call it is superior, but it is more work. Air Admittance Valves are acceptable but only if you have true island, and you can walk all the way around your kitchen sink.

The AAV should be installed as high as possible. If there is room behind your sink, above the height of the sink's drain, put it there.

The previous install is acceptable if 1) the trap is accessible, 2) easily removable, 3) the fixture outlet pipe is no greater than 900mm (The vertical pipe from the sink's drain to where it enters the trap) and 4) the fall of the horizontal pipe from the trap weir to where it enter's the stack (the "collector pipe").

This last one is where you are getting your 6ft. from. If the pipe has minimal grade (1/4" per foot) and is 1-1/2" in diameter, than in theory the pipe has not dropped by more than its pipe diameter. If the grade is greater than 1/4" per foot than the 6 feet doesn't apply. try to think of it as the pipe cannot drop more than one pipe diameter measured from the trap weir to the stack, and not by maximum trap arm distances.

[Ducay]

Originally Posted by sa226

Thanks guys.

So, given my situation, is the "accessible" trap and AAV the preferred method? Or just basically not messing with what worked before?

I'm just thinking down the road when the basement is finished, having to install little trap doors in the ceiling the be able to access the P trap.

The trap and drain are all 1.5 inch, which I guess would mean the run is 6ft ( 6, 1\4's?)

So if I'm understanding it correctly to prevent siphoning, you can't have anywhere downstream of the trap where the water "fills". If you have drain water crashing down like a waterslide into a 45 elbow or a sanitary T it will created a vacuum and siphon the trap. Whereas if its a nice slow trickle and 1/4inch per foot, air can still get back to the trap and its just gravity doing its thing?

I would say you are fine to move the trap to where it is accessible, which is preferred.

The trap location currently was likely to allow for no venting (there is a prescribed distance and rise/run, and has to be within X inches of the end of the run at the main trunk line) back in the day before AAVs or good AAVs. Having the trap in the floor area serves no purpose. Personally, I would put the trap in the cabinet, plumb in an AAV, plumb in a cleanout after the trap, and leave it at 1.5" pipe (unless you can replace the entire run with 2" easily).

[sa226]

Haha okay thanks.

I've got one guy saying don't mess with what was working and one who is saying move it up and install an AAV! It is all good advice, and kind of confirms my previous thoughts. I just haven't done a ton of plumbing and don't want to screw it up.

I'm aware that the loop vent is the preferred method, but it just isn't practical given whats available. We have two sinks in our kitchen. The main sink is on the wall and has its own vent. This island sink is just a 15" bar\prep sink, so it won't see a very high volume of water.

I just want to get it right, so I don't end up on one of those youtube "DIY Plumbing Distater!" videos. Or have Mike Holmes show up and tear my house down.

[sa226]

Originally Posted by Ducay

I would say you are fine to move the trap to where it is accessible, which is preferred.

The trap location currently was likely to allow for no venting (there is a prescribed distance and rise/run, and has to be within X inches of the end of the run at the main trunk line) back in the day before AAVs or good AAVs. Having the trap in the floor area serves no purpose. Personally, I would put the trap in the cabinet, plumb in an AAV, plumb in a cleanout after the trap, and leave it at 1.5" pipe (unless you can replace the entire run with 2" easily).

I think thats exactly the reason, in the 90's and ealry 2000's I think that was the general method, but I don't think it is code for new construction anymore. My main floor half bathroom also has the pedestal sink P trap under the floor.

[topfiverecords]

Extra advice to add, don't stand on the sink after you've completed the work.

[speede5]

Originally Posted by sa226

Haha okay thanks.

I've got one guy saying don't mess with what was working and one who is saying move it up and install an AAV! It is all good advice, and kind of confirms my previous thoughts. I just haven't done a ton of plumbing and don't want to screw it up.

I'm aware that the loop vent is the preferred method, but it just isn't practical given whats available. We have two sinks in our kitchen. The main sink is on the wall and has its own vent. This island sink is just a 15" bar\prep sink, so it won't see a very high volume of water.

I just want to get it right, so I don't end up on one of those youtube "DIY Plumbing Distater!" videos. Or have Mike Holmes show up and tear my house down.

Nice to have options. The right way is the one that suits your needs/concerns. (future access) Given what you're trying to do moving the trap up is a good option. Just spend the money and get a good vent. And draw it out and run it by a plumber before you commit.

[sa226]

Thanks again.

Just finished up before the game. Ended up moving the trap up and going with a ridiculous 45$ piece of plastic (Studor Vent).

I admit I didn't draw it up and run it by a plumber but I've put in an obscene amount of research time and I think the design is fine with rise\run stuff and cleanouts and all that. There are a couple of things that I'm not happy about , but everything is draining fine and the trap is holding water.

Next up is to try standing in the sink.

[Ducay]

Originally Posted by sa226

Thanks again.

Just finished up before the game. Ended up moving the trap up and going with a ridiculous 45$ piece of plastic (Studor Vent).

I admit I didn't draw it up and run it by a plumber but I've put in an obscene amount of research time and I think the design is fine with rise\run stuff and cleanouts and all that. There are a couple of things that I'm not happy about , but everything is draining fine and the trap is holding water.

Next up is to try standing in the sink.

Good stuff. There are indeed a lot of rules and things to follow, but at the end of the day for a simple sink, as long as you have a down slope and a vent, it'll be fine.