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Bathroom Drain Venting Help

Discussion in 'Plumbing and Central Heating' started by dazjstuart, 5 Oct 2020.

  1. dazjstuart

    dazjstuart

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    Hi,
    Looking for a little help on the drainage system for my bathroom. The first picture shows how everything is at the moment. The bath and sink drain separately to the outside grey water stack which is vented at the top. The toilet drains out the 4'' cast iron pipe but also seems to have a vent that ties into the same soil stack a little higher up. Second photo shows the arrangement outside. Probably worth noting, this is a "standalone" system in the bathroom, nothing else ties into these stacks other than what you can see, kitchen drains are round the other side of the building.

    [​IMG]

    [​IMG]

    My drawings aren't to scale but the main point to take from the bath / sink arrangement is that they go out to the outside stack separately. This system seems to work but I do occasionally get a smelly drain from the bath or sink, and the bath is quite slow draining.

    I am about to start renovating the bathroom. Installing a new bath and a sink unit, what I was wondering is if I can tie the sink drain into the bath drain and have them both go out the same cast iron pipe? My plan would be to install a sanitary tee between the bath trap and the cast pipe then tie the sink into the tee, I would then just block off the cast pipe that the sink currently goes to. That way I could run the sink drain as low as possible along the back of the bath (allowing enough fall). See below drawing of my proposal.

    [​IMG]

    The reason I would like to do this is the drain for the sink is currently quite a bit higher up and I need to box in some of the pipework, and want to avoid a massively high box (I know the drawing doesn't show that, in reality the toilet and a space with pipe box will go between the sink and the bath, this drawing is just to keep it uncomplicated). Should I be concerned with drawing a vacuum on either the sink or bath with this set up? My own thought is no as the big vented cast stack is only about 2ft away on the outside of the wall but what is the reason for the separate sink and bath drains in the first place?

    Now moving onto the toilet. In the first drawing above you can see the toilet joins onto the cast pipe with a standard flexi pan connector at the moment. On the cast pipe there is a second pipe sticking out the top that from what I can see is a vent that simply goes outside and joins into the stack a bit higher up. What is that for? Seems quite unusual to me, I'm not a plumber but I thought the toilet usually runs into the stack and the stack is vented so you are good to go, no need for other vents unless you have other toilets (which I don't). What I would like to do is below.

    [​IMG]

    My reason for this is I want to cut the cast pipe flush with the wall (it sticks out around a foot at the moment) this would remove the bit with the tee to the vent. In my new bathroom layout this will all be behind the bath so I need to make the pipework as space efficient as possible so it all fits in.

    So what I am basically asking is, if I get rid of the separate sink drain into the stack, and rid of the additional vent for the toilet (both of which seem quite unusual to me) am I asking for trouble? If so is there anything I can do about it (other than plumbing it back how it is at the moment).

    Hopefully this is clear, if any other information is required I shall endeavor to provide.


    Thanks in advance.
     
    Last edited: 6 Oct 2020
  2. sircerebus666

    sircerebus666

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    Can't see your pics for some reason
     
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  4. dazjstuart

    dazjstuart

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    That's weird, I can't see them on my phone either but can on my laptop... I just copy and pasted them in and that seems to be working.

    What do people on here use for photo hosting as historically forums didn't like you saving photos within posts as is uses up server space (maybe thats not an issue now a days?). I used to use photobucket back in the day but like all of them they end up deleting your photos or making you pay...
     
    Last edited: 6 Oct 2020
  5. nearthemark

    nearthemark

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    Really odd, I can see your pics on my phone but not on the PC.

    I wonder if the only reason that the room smells a bit, and that the bath is slow to drain, is because the U-bend is blocked or not working in some way? In theory, the water in the U-bend should completely prevent any nasty niffs coming up?
     
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  7. dazjstuart

    dazjstuart

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    It could be, it only happens very occasionally so I haven't spent much time trying to get to the bottom of it, I'll have a look at the u-bends when I take them off. As I described in the OP as the sink drain comes out a bit higher than the bath one there isn't much run on it (+/-8ft horizontal section) and the person who installed it didn't do a good job, no clips so the pipe sags in the middle and runs slightly uphill towards the outside wall.

    I'm more concerned about what the weird second vent is for in the toilet drain and whether my plan to remove it will cause problems.
     
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