Waste pipe height re: new kitchen sink..

[construct]

I'm in the process of replacing the existing metal sink with a Belfast unit, and the waste pipe has been chased into the wall behind the current units. It also appears that allowing for the depth of the new sink, the replacement P trap will sit/connect about 50-60mm lower than the waste pipe itself.

Is it practical to have a height difference at the beginning of the water flow, or will I need to re-chase the waste pipe again?

 

[kevplumb]

cut it out and remake the waste

saves having to pull it out when it wont drain

 

[construct]

cut it out and remake the waste

saves having to pull it out when it wont drain

Cut what out? The waste pipe is chased into the wall at a fixed angle, are you talking about inserting a bend lower down and meeting the connections earlier?

 

[kevplumb]

yes

 

[construct]

Right, having lined up the new sink unit with the existing waste pipe, you'll see from the pictures that the height difference is always going to prove too great to work, so I'm considering two options and would appreciate any advice offered regards the best way forward:

1. Chase out a whole new route at the correct height and replace the existing waste pipe in the process.

2. Put the units against the wall, and run the new waste pipe inside the rear of the units and out the end into the soil pipe? (which will eventually be boxed in)

See images below...

 

[kevplumb]

2. Put the units against the wall, and run the new waste pipe inside the rear of the units and out the end into the soil pipe? (which will eventually be boxed in)

thats the way to go

will be worth putting a tee with an acess cap at the sink end as well incase you get a blockage

 

[Hugh Jaleak]

If you can join onto the existing pipe at the lower level before it enters the stack then I would do so. I wouldnt recommend disturbing the existing boss connection or it may leak..... If you are using solvent for the new run I would suggest incorporating a rodding access, if it ever blocks it will be a pig to get to otherwise.

Its your preference whether you run the new waste through the units or chase the wall, but Id take the first option! Most have a false back so you could conceal the run behind that. Fit your waste against the wall, then notch the units to allow them to fit flush to the wall.

 

[TicklyT]

Long horizontal chases are a bit worrying - especially if you end up cutting a 2" deep chase into 3" thick blockwork..

 

[gigz]

As Hugh says, most units have a 70mm gap at the back, cut the pipe (carefully) a couple of inches from the boss, two 45s (better than 90s) and an access tee.