Waste water not draining.

Sounds as though you may need an Air Admittance Valve. Its job is to let air in and is usually used if the stack can't be vented or in situations such as yours.

Has it always been like this, or has it got worse with time?

I'd have said it was more likely to be a poor gradient and/or partial blockage with gunk. I've had as much success with washing soda as with expensive branded cleaners (YMMV). Bleach (used neat) is sometimes effective against biofilms. Let it soak overnight, then flood and use plunger. Nothing much will dissolve hair.

Most pumps made for waste water are rather big lumps. I think you really need to diagnose the root problem.

Eh? Dissolved caustic soda will, given time. (I used a pig-bristle brush to apply a caustic-based cleaner, and the bristles first turned to a mushy goo and then dissolved in use.)

Thomas Prufer

Yes, but that was a) being agitated (which hair in a drain isn't being); b) not covered with gunge which protects the actual hair from the cleaner.

Enough of it, left long enough, will eventually dissolve it, as will conc sulphuric (preferably not at the same time ...)

To the OP: How easy would it be to take the pipes apart and flush them out properly? Or even replace them with new ones - which will probably last a few years until the problem recurs.

Sounds to me more like a problem with the geometry of the system. We have a similar problem with the traps in our motor home which require a significant head of water above them before water will flow freely (or you give it a bit of a plunge to get it started and then it races away).

It may be that a shallow P trap would help but it's not always easy to change these things post-installation.

Tim

I use caustic crystals followed by a kettle of boiling.

Wear glasses.

It boils and creates pressure in the trap as well as dissolving the muck

Thank you for your suggestion. The venting is a problem, so I will give it a go

- Many thanks

Sounds like the two basins, shower and bath all sharing a single waste boxed in above the floor with naff all fall and 5 bends (not counting traps...) that I have just unblocked. Bottle trap on the bath (doh!) was clogged with hair, pipework despite only nominal fall and occasional up hill just had a mm or two of gunk inside, but the bend half buried in the wall was half full, removed what I could of that and ran a stiff wire with a U shaped end back and forth along the 2' length of pipe through the wall to hopefully break up anything along there so it'll flush out.

Standard OD for modern 40 mm - 1 1/2" solvent weld waste.

How old is this system? The above mentioned pipework is 43 mm OD but most definately push fit, hence being able to take it apart clean and reassemble, it's probably about 30 years old. Modern push fit is 41 mm OD.

Concentrated nitric acid works fine too.

Not great for plastic pipes tho.

Plumber mate of mine used to tip an entire winchester of conc nitric down any drain that was having a problem. That was in the days before plastic plumbing tho and he wasn't paying for the nitric acid either, got it for nothing at work. He did the maintenance of all the plumbing there and in the staff houses too.

Thanks for your suggestion and advice.

Hi Dave It clearly printed on the pipe 43mm. And only 4 years old! Its strange as I am aware its normally 40mm for waste pipe. its not blocked because since its been installed I've had to use a plunger to clear it. But only one plunge does the trick so sounds like an air blockage problem like the first reply suggested.

I wonder if this could be a sticky HEPVO trap? Perhaps coupled with air admittance issues.

Nope :-) 40mm is the nominal size, but the pipe isn't that size. Solvent weld is IIRC 43mm, pushfit a little smaller (41?)

We had problems with the old shower here. (predating us, shower probably installed in the 1990's but using waste pipes that look like they had been there longer. We moved in in 2005

It had a long run across the bathroom under the floor (6metres or so). It never drained properly- it would fill up the tray and then suddenly drain out, sometimes you had to force it.

When I ripped out the bathroom I discovered the reason (as I suspected) The waste pipe was badly installed and had developed a sag such that it held enough water to form a complete or partial air pocket between the shower trap and the sagging point.

Correct.

Unless you have 30 year odd old pipe that has 42 mm stamped on it, measures 43 mm and is push fit. Looking at you Marley Extrusions ...

Quite likely, plumbers tend to ignore supporting wastes as the maker recomends. Pipe doesn't sag on installation but given time and hot water it does and quite a lot given a chance.