Guys, I am a reasonably competent DIYer, but not an expert on plumbing. Currently gutting and completely relaying out my upstairs bathroom. Bath will be 4m from stack, so I will be running waste in 50mm into a new boss on the stack, and teeing in basin half way along the run and using an anti-vac trap or AAV. Solvent weld throughout. Hoping that will be OK. My problem is with the 40mm shower waste which is next to the stack. I have two options Run it into an existing 30 year old push-fit boss, which looks in reasonable nick apart from a greasy residue around the old push-fit seal – not sure if this old plumbers grease or an oozing joint. This would give the shower a dedicated access to the stack, but I am concerned about that greasy residue and long term reliability. And I would need to connect push fit pipe to solvent pipe with a compression fitting. All this then buried under floor beneath the shower. For obvious reasons I would prefer a solvent weld solution. Second option is to tee it as a third fitting into the new 50mm run (solvent weld). But with the bath furthest from stack and this tee nearest stack will I be risking siphoning of the shower seal? There’s nowhere obvious to fit an AAV. Would it help if I minimise the fall past the tee (18mm/m)? Or use 50mm as far up the shower line as possible? Which option should I go for? Any other solutions?
Just buy a new rubber bung for push fit boss, if you thinks it's iffy. Why push fit with solvent pipe, why not complete new run of solvent pipe for shower? You can get McAlpine Multifit Adaptor T28M for joining solvent/pushfit pipe. No issues with AAV on 50mm pipe.
If your fitting an avv in the run it shouldn't cause a problem fitting the shower on to the new run. A dedicated plumber will be along at some point to confirm this.
Time to put the old fool out to grass,, getting confused here, with the basin AAV , should be ok with shower. How far is shower pipe from 30 year old push-fit boss?
Thanks for your quick replies. Taking questions in turn I would have tried to source new seal, but can't identify the manufacturer of the boss. It is grey, and is marked "Series Ten", but otherwise just a patent number and a BS number. I do plan to use as much solvent pipe as possible in the shower run, which is why I don't like the old seal and compression fitting But I can't see how a multifit would fit this boss. Can't think how to describe it, but the outer edge (the edge the SW pipe would first encounter) is folded inwards around the entire circumference. A bit like the bottom edge of a jam jar lid. Will try to post a photo later Phil : I don't properly understand AAV's but believe they work by letting air into the branch that is in danger of getting siphoned. So will an AAV on the basin branch help the trap on the shower branch? KIAB : I understand your post #4 - that's what I'm afraid of. But don't understand why you withdraw it in post #5. I would like it to be OK, but why do you think it would be? The shower pipe will of course go into the 30 year old push-fit boss, and then run for about 1metre to the trap, with a couple of 135 bends along the way. Perfect arrangement, provided it doesn't leak! Thanks for your help. Will go and take that photo.
Sorry,the way I read your post, I though you were joining solvent & push fit pipe together, hence the Mcalpine Multifit connector I suggested. Post 4: I remembered after posting that you also add a AAV on sink, so shower should be ok, but you only have 10 minutes to edit your post, had phone, doorbell going here & didn't have time. Seldom do those old push fit boss bungs leak, as there usually a slight fall on the pipe. so any water goes down the stack, rather than run back.
KIAB : As far as I can see, all I can do is use a piece of push-fit pipe to connect to one end of a compression, then connect the other end of the compression to a solvent weld pipe. Which leaves me with 2 compression joints and a dodgy push-fit joint under the floorboards (did I mention I'm tiling it?). Which is what drives me to the 3 into one 50mm solution, and the siphoning question. Sorry, I haven't explained this very well, have I.
Oh! that sort, can't change the rubber on those, just a bit of lube on the pipe to ease it in, watch you don't push the rubber into stack. Some bosses use the type of bung below.
Yes, I've seen those and drooled over them enviously. So which do you think is the lower risk solution? The old push-fit with a compression joiner, or the nice new 3 into 1 50mm pipe that might siphon the shower trap? Or am I missing something else?
Tilting it, risk of it leaking, if access was easier,(from below) & you could replace all pipe work with solvent I go with the 30 year old boss. But, for ease you have to go with the 50mm, you have the AAV on the basin, plus stack pipe vent, most likely perfectly ok,but I'm still wary about it, you don't want the sewer smell in the shower.
KIAB - this is a bit of an off the wall idea. But what if I run the shower waste into the new 50mm as a new branch (option 2 in original post), and then counter the tendency to siphon by running a vent pipe from the shower line to the stack via the old pushfit boss. Please see attached sketch. I may have to run the vent in 32mm to get the pipework to fit in the void. Also, there will be only 200-250mm between the vent boss and the waste boss. Will that matter?
KIAB, thanks for your input. I thought you might like to know what I have eventually gone with. Given the space and access I have available and the some of the comments from other forums I have dropped the idea of a vent pipe and gone instead with a waterless Hepvo type trap for the shower. I wasn’t keen on these originally because people say they block, but my thinking is that it will be a lot easier to unblock one of these if I have problems than it would be to correct a dodgy vent pipe installation. Hepvo imply their trap never blocks, but that’s not what some people say. So I will probably go with the Wirquin one available from Screwfix, because that is built in to the waste fitting and can be unblocked from inside the shower tray rather than by removing the fitting from underneath. Thanks again for helping me work this through.
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