Kitchen sink - shallow trap suggestions?

[tartanterror]

Hi

Moved to a new place and been having a bit of bother with the sink. It seems like the drain point is a bit high so there’s not enough fall.

Im planning a new kitchen so want to try to fix this problem with the new layout. I can’t move the sink from its current position so how do I lift it up?

I think the current sink is 170-175 deep so I can choose a shallower version. Regular small sink options are 150. But I could choose 120 deep - would that be odd/too small in a one bed flat?

Another option is to get a compact trap which will save some space compared to now - but it seems like the overflow connection pushes the level down. Any way of making that as tight a junction as possible? Seems like the current arrangement loses 30-35mm of height. Anyone know of a particularly small overflow connector?

or last - but hoping to avoid if it’s likely to block/go wrong - a really shallow trap which would still allow one dishwasher connector?

any suggestions thanks?

If you stand back and take a wider pic, down to the floor and up to the worktop, we can visualise how it fits into its surroundings

Same with the stuff under the sink

Thanks

The drain point is in a different room so I can’t get you a wider shot - the drain runs 3m to the right along a wall in a straight line. Im getting a new sink so there is no point getting a pic of that - it will be a 500 wide cabinet and backing on to the wall where the waste runs…

Will the new sink be as near to the wall that the pipe goes through as possible whilst still being in the kitchen?

No. And it can't move closer to the wall/be in a corner.
Why do you ask?

Diagram as my test/numbers explanations dont seem to be clear enough…

Great help, shows more clearly that moving the sink is not an option (though getting one with the waste positioned as far over as possible could help a bit). OK, mark the point at the lower edge of the 3m pipe where it exits the trap. Then draw a horizontal line across to the sink waste. That's your standing water level in the trap. The height of that level is your deciding factor. Work it out from there.

Is the lower hatched area a cupboard void where you could locate an extra trap for the dishwasher and/or a DIY modified trap for the sink?

To be clear re my comment on your diagram, your design needs to raise that trap standing water level to the highest level that will still work. You are absolutely right not to compromise on the 3m fall. The physics is non-negotiable.

I am not trying to be annoying, i was just trying to make sure there really is no other option because i really think a shallow sink will have a lot of functionally annoying consequences. It would really irritate me and would put me off buying somewhere.

Sure - but the 150 depth that seems to work is a “standard” compact option. (I took on board your previous point and have abandoned the 120 option)

Do you think anyone would really notice 150? How deep is your current sink? Or your friends’?

If anyone has a thought about it - I suspect it’s more likely to be that they don’t like inset stainless steel sink/drainer and would want a fancy butler or under mount instead?

Fortunately the flat isnt for sale and wont be in the lifetime of this kitchen - hence my caution about adjusting the drain pipe… The next installation can cut into the cast iron and live with the risk of hideous blockages rather than me 🤣

Yes thats a row of cupboards coming out towards us. I could use a wider worktop and get more space behind the units on the wall with the drain if I need to

Also getting the appliance connection out of the way - maybe I could add this the straight run of pipe and not have the appliance trapped at all?

https://www.screwfix.com/p/mcalpine-v33s-compression-domestic-appliance-tee-piece-connector-white-40mm/4167P

I wouldn't risk the dishwasher without a trap. I think the hose is pumped empty, which would allow sewer gas to enter the kitchen. I'd put a standpipe and trap for it in the cupboard void. You can get drain hose extensions if it won't reach (or even trap it before the sink).

Fair enough. I am impressed with your making your own waste trap solution. I also agree that the dishwasher waste needs a trap.

Thanks both! I will make some tweaks and maybe try another diagram at the weekend.
Also I realised I need to think about the flooring - if I tile the kitchen all the levels there will go up relative to the drain point so that will also help

Ooh sorry - another thought - how about I modify the trap i was thinking about before instead of starting from scratch? Maybe using solvent waste pipes and bends? Raising up the outfall of the trap (as long as I make sure the dishwasher pumped arrives at its connection point from high level to avoid backwash?) should do the trick?

I'll follow up with a diagram, but the dishwasher inlet must be clear of the standing water in the trap. This lowers your whole assembly, and hence your potential fall, by the diameter of the fitting (presumably 32mm). You will need a separate dishwasher trap. Otherwise yes, your plan should work.

I'd suggest compression, not solvent or push-fit. It's more forgiving, and allows disassembly for alteration or cleaning. You have a height problem, not a girth problem, so don't need the sleeker profile. I'd get all the fittings, maybe a couple of the same or different traps, from one good-quality manufacturer (eg McAlpine). Mix and match until you get what you need.

The P-trap in your diagram has a longer leg on one side of the U than the other. Other makes can be more pronounced than this. I think this would enable you to separate the U, and screw its longer leg straight onto the waste. This could give you enough room to screw the shorter leg straight onto an elbow going onto the horizontal pipe. This does not provide a dishwasher connection, which would need a separate trap. I think you are stuck with the latter anyway. I can do a couple of diagrams this evening.

Sorry to go on, but any idea of the dishwasher inlet being below trap water level will not work. Not even if it arrives from higher up. The appliance would risk having to pump the trap contents (working against the 'U') as well as its own hose contents. Too much room for failure. You have the space to give it its own standpipe - I don't see an alternative (except a macerator, which is best avoided whenever possible).

I thought I would check my figures again and it seems that the 25mm/m rule is the recommended fall ie 1in 40 - which for 3m is 75mm.

However the minimum fall is 1in100 - which would be 30mm.

So if I go with the standard 150mm deep sink, trap (above with appliance connector) and all parts off the shelf I will be well above minimum and won't need any special messing around.

Am I missing something?

Can you achieve close to 1 in 40? I wouldn't go far under (or over). Get as close to it as you can.

Yes - 75mm fall is 1 in 40

Well if you go for compression fittings you can fit it, tighten it all up and test it live. You can then modify it and go to plan B if anything doesn't add up. Though that shouldn't happen if your parameters are correct. If you do need to minimise the drop, you could shop around for the shortest sink waste you can find (the plughole bit, usually a basket type for a kitchen). And an adjustable trap, where the exit elbow from the U can slide up and down or be cut.