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Best solution to slightly rising waste pipe problem

Postby jamezm » Sun Jan 24, 2021 9:58 am

Hi guys. I moved into a house where the kitchen was moved from an upper floor to the ground floor, at the back of the house, so there was no existing soil pipe near to the kitchen double sink and dishwasher. In their infinite wisdom, the plumbers who set this up ran a very long length of waste pipe from the kitchen (at the back of the house) to connect to the waste at the back of the toilet / WC at the front of the house. They used 40mm all the way. I don't know the exact length, but it's the full depth of the house - minimum 7 or 8 meters I suppose. Apart from the fact that this must surely be too long a horizontal run, with very little drop, there's a 1m/2m section towards the end (where it approaches the WC waste) where it's actually going slightly upslope, in order for it to reach the height where the inlet waste connector sits at the back of the toilet. I can't see any venting / AAV.

Inevitably, of course, most of the length of this waste from the kitchen is permanently part-filled with standing water. So the double sink takes a long time to empty and the dishwasher (which shares the sink trap) often backs up into the sink, and there's a fair amount of gurgling from the double sink as it drains. All far from ideal. Before I saw the upslope, I thought this was just from a standard blockage, so I got a rodding access point installed halfway along the run, but that really doesn't help. It's not a blockage, it's standing water because of the upslope.

Anyway, I want to find a (cheap and easy!) solution. Realistically, I can't see a way to fit a waste pipe at the back of the house - there's just a gutter run back there. I also can't see a way to raise the waste pipe any higher where it currently starts to drop, as there are kitchen units in the way. However, there is a basin sink in the WC that has a small 32mm waste so maybe there's an option to redirect the kitchen waste pipe into that, as at least it would then keep going downhill. So, I'm guessing there are three options:
1. install some kind of pump somewhere to force some pressure into the waste to get it over the hill
2. replace the toilet waste so that the inlet for an extra waste pipe is closer to the floor (does such a part exist?)
3. redirect the kitchen waste pipe into the WC basin waste instead of the toilet waste

Am I missing something? Any other ideas please? I've attached a rough diagram but it's not to scale - the waste run is actually longer than that.
waste diagram.png
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Simply Build It

Postby stoneyboy » Mon Jan 25, 2021 11:01 pm

Hi jamezm
Suggest you upgrade the basin waste to 40mm and Reed the kitchen waste into it.
Regards S
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