Sink & Washing Machine Drainage.

Discussion in 'Plumbers' Talk' started by FagCardFreddie, Jan 11, 2013.

  1. I purchased a flat recerntly that used to be a two story apartment in a block of flats and has been converted to two flats.

    As a part of the conversion they put the kitchen at the back of the block. I have since realised that this is the only water (i.e. sink, washing machine, shower, toilet etc. etc. etc.) at the back of the building as the main drainage is at the front of the block and all the other flats feed into that.

    The problem I have is that when I purchased the flat the sink and washing machine would not flow away as the previous tenants had used cooking fat etc. and poured it down the sink and it solidified in the waste pipe leading to the front of the building. I have solved this problem by cutting out the pipe and replacing it.

    My question is: 'how do I prevent this from happening again as I cannot get much of a fall from the back of the building to the front as there are joists in the way and in some places the pipe would run slightly uphill?'  I called a 'plumber' in who suggested a pump but I do not like this idea as a) it is noisy and b) expensive. As I have the floorboards up from the back to the front of the flat at the moment I would like to solve the problem once and for all although I am aware that no solution will legislate for pouring cooking fat down the sink!!!!!!!

    Now for the silly question: If the water from the sink and washing machine goes through the 'U bend' under the sink which has to go 'uphill' would that same water be able to go slightly 'uphill' through the waste pipe? My logic seems sound but I am not sure if it would work in practice! Any advice would be greatly appreciated.


  2. anthonyw

    anthonyw New Member

    if you can't run the waste pipe under the floorboards, due to direction of the joists, I think you've got two options.  The waste water won't flow uphill so you're looking at a macerator (pump) or running a waste pipe, clipped to the wall above the floorboards, through the flat and boxing it in.  The only problem is that there is a maximum length you can run 40mm waste pipe horizontally, three metres maximum.  Once you go beyond three metres you have to increase the size of the waste pipe and ensure that you mantain a minimum of 1 in 40 fall.  Nobody likes the idea of a macerator, they are a last resort, so you have to decide between a macerator or a waste pipe running through your flat.  What about your toilet, how is that connected to drainage?  You mention the toilet is at the rear of the property, can't you connect into the soil for the wc?
  3. joinerjohn1

    joinerjohn1 Screwfix Select

    Easily answered. It won't block up again due to a build up of fat, because you are not going to be daft enough to pour hot cooking fat down the kitchen sink ,, are you ? ;)
  4. Captain Leaky

    Captain Leaky New Member

    Water CANNOT flow uphill. The U bend is part of a downhill run of pipe work.
  5. Dereekoo

    Dereekoo Member

    But it can be driven up a vertical or sloping pipe if the top water level upstream of the pipe is higher than the pipe itself. Thats why a sink full of water can empty itself up a U bend
  6. Hi AnthonyW,

    Thank you for taking the time to reply.

    The toilet and shower are at the front of the building (where they should be), it is only the kitchen that is at the back of the building. The waste cannot be surface mounted as it would go across the top of the stairs on one side and bedroom and lounge doors on the other. How this conversion ever passed building control I will never know, but I do have a certificate for it!!!!!!!!

    Dereeko mentioned that water can run uphill if the water waste source is higher than the pipe itself. The waste pipe itself (it's about two and a half inches in diameter) enters the main stack (at the front of the building) considerably lower than than where the pipe goes below the floorboards (at the back of the building) but it does have to go slightly 'uphill'  and down again where the joist is. The joist has been cut into, but I cannot cut any more out of the joist for obvious reas...... aaaaaaaaaaaaaaargh!!!!!!

    Am truly grateful for everyones input.

  7. Captain Leaky

    Captain Leaky New Member

    But the overall flow is still downhill ;)
  8. snezza31

    snezza31 New Member

    Plus the fact that most of the muck/grease/fat will lay in the pipe at the lowest point due to inadequate rate of water flow. It may seem as though the water is flowing uphill, but it only appears that way! Captain Leaky is correct, the overall flow is downhill.

  9. So, Captain Leaky and Snezza31, IF  the overall flow is downhill, even though it may go slightly 'uphill' in places, will it work O.K.?  Provided of course that no one pours cooking fat down the sink which would probably block any drainage system up anyway!!!!!!
  10. Captain Leaky

    Captain Leaky New Member

    No. Any uphill runs will collect the fat and sludge and become blockages.
  11. Glad its Friday

    Glad its Friday Active Member

    This must be the dullest post ever!
    The Captain told you - water doesn't flow uphill.  Any sludge will collect in the lowest point.
    Just sort the slope so that ther is a continuous fall otherwise you WILL have problems later on.
    That's me done, anything good on motd tonight?
  12. Dereekoo

    Dereekoo Member

    Depends how fast the water flows whether the sludge/fats collect in the pipe.
  13. Captain Leaky

    Captain Leaky New Member still builds up though ;)
  14. Don't put yourself down. Despite yours being the dullest post ever I accept that you did try to help, and I thank you for that.

    Hope you enjoyed Match of the Day?

    Actually, Captain Leaky said (12 Jan 14.26), that it would work 'provided the overall fall was downhill'. I think you misunderstood him!!!!!

    Hope you're not an Aston Villa fan lol?

  15. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Whoops! Wrong end of the stick springs to mind.
  16. Lol.

    Thanks everyone for your input although I am not an awful lot nearer solving the problem.
  17. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    Your water will only run uphill if being forced uphill by more water. Any dips will keep water. The U-bend is such a dip, level on both sides.

    Best you can hope for is your gradual slope being perfectly straight. No dips or rises. So lots of brackets and a perfectly straight line. That way your entire run after the U-bend(trap) will empty. (And rinse through as often as possible)

    Mr. HandyAndy - Really
  18. FagCF, since you are basically saying that you cannot cut into joists to get a better slope, and you don't want a macerator, will you "get away with it"?

    Probably. As long as you don't pour disgusting stuff down the sink, and you flush it through thoroughly, and you pour some nifty caustic chemicals down there too. But keep the floor boards loose 'cos you'll probably have to clean/replace the pipe every - ooh - year or so.

    As Mr Ha says, if it's a choice of 'slighly sloping down with the odd slope up', or 'completely level', I think I would choose the latter as well. In theory it'll drain out pretty much completely. (Then use flushes, chemcials, etc at regular intervals...)

    Can you fit a larger pipe into the run - say rainwater downpipe, solvent-welded?

    Or, is there a drain in the ground on the kitchen side of the flat? Since the whole thing is a bodge already, I reckon all you'd have to do is use rainwater downpipe pipe for your 'soil' pipe down the outside wall instead of 4" pipe (downpipe is about 2 3/4"?). Make sure it's proper drain, tho', and not a soak-away...
  19. Mr. Handyandy

    Mr. Handyandy Screwfix Select

    No DA. Not level, straight. With slope.

    Mr. HandyAndy - Really
  20. I think the OP has already said that's impossible. If he could have fitted it on a straight slope, he wouldn't be on here askin'.

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