Inserting a new section into a plastic stack pipe

[RolandK]

Hi there,

I need to make a connection for a kitchen sink waste into an existing plastic stack pipe on the ground floor. The problem is I can,t come out of the side of the pipe as the connection would foul the back of a bulit in dishwasher. Idealy I need to make the connection towards the back of the pipe but don't have working space as it's faily tight in a corner. Is it possible to cut a piece out of the stack (supporting it as necessary!) then slide in a new section with the new connection fitted. This would obviously need some sort of sliding couplings but not sure if such things exist? Or any better idea gratefully received!

Cheers,

Roland

 

[justlead1]

Hi. Check out whether the the joints either end of the soil pipe are solvent weld or "O"ring. If "O" ring you may well be able to fit a stap on boss and twist the stack (after knocking a bit of mortor/brik/block away) to get it at 45 or 90 degrees to miss obstruction.

 

[kirkgas]

search on the plumbers merchants siyes for 110mm short boss, (which has a connection for your sink) and also a 110mm slip collar (which is what you will need so slip up the pipe, insert short boss and bit of pipe then slip the collar back down onto the pipe, then swivel the boss round to where you want it,
PS you also get 38mm M/F bends (M/F is for male/female, which allows the male end to go into the boss to shorten down the overall dimension of the bend)

 

[RolandK]

Hi,
thanks for the reply,

it's difficult to see the stack connections as it's boxed in apart from the bottom 3 feet. In that the existing waste seems to be solvent weld and I can just see a bit of the upstairs toilet connection which might be welded too, difficult to see. If that is the case looks like I'm out of luck just twisting the stack. If I could twist it would it stay leakproof at the joints? It's the original stack pipe and about 25yrs old.

Cheers.

Roland

 

[RolandK]

Thanks Kirkgas,

I was thinking of leaving 4-5 inches of the existing stack in the coupling where it goes into the concrete floor, Then cut about 12 inches out of the existing pipe to take the new section with the boss as you desribe. That means I take it, that I'll need 2 of those slip rings, one at each end of the new bit? Are those short bosses solvent weld? The male/female bend sounds useful to keep the whole thing compact. I take it then that it's ok to have a 90 deg bend just as it enters the stack.

Thanks for the info. which will help if I would like to do it myself, else I might chicken out and get a plumber in!

Cheers,

Roland

 

[kirkgas]

you can use 2 slip collars depending on what height you can get to, or just 1 and the boss, using a M/F bend right into the stack is fine, the boss is solvent weld (the ones i have used anyway)

 

[RolandK]

Thanks again Kirkgas,

I see what you mean by just using 1 slip collar and the boss. Is the boss a solvent weld onto the 110mm pipe or is it a ring seal with solvent weld just for the elbow into the boss? I assume the slip collar is a ring seal so you can slid it up/down the pipe. I think I may have to put the sink waste pipe out thru the wall, take about a mtr of pipe along the outside wall and then back in behind the stack to get the clearance even though this sounds bit crazy! Any tips on how to stop the stack collapsing when a bit is cut out of the bottom?

Cheers.

 

[kirkgas]

you will be very unlucky if the stack collapses, it "should" be clipped, however if you are cutting between clips it is possible that the upper section can slip down a bit, but TBH it is unlikely to move much

 

[RolandK]

Thanks for the replies,
I'm going to tackle this at the weekend so fingers crossed! I'll try to support the stack a bit as there don't appear to be any clips holding the stack at all. I was thinking of pulling the first couple of feet of the existing stack out of the connector in the concrete floor and replacing that bit of pipe. I think the brown connector in the floor is probably a ring seal? It's around 25 years old so is it OK to disturb it or is it likely to leak when the new pipe section is inserted? That is would you advise leaving it undisturbed as much as possible?

Thanks,
Roland