Waste pipe problems

[KJH]

Hi

Please bear with me as I am a complete plumbing novice but have a bit of a problem I hope you can help with.
We had a new bathroom installed (by a friend of a friend - big mistake!) a few months ago and the shower has never drained properly. To get it to drain you have to fill the sink then let the water out so that the shower drain gurgles - then the shower will drain. Obviously during the day the basin gets used for handwashing etc so only small volumes of water are discharged and this seems to be what causes the shower to then drain too slowly. Only the large discharge from the sink 'clears' the shower drain.
The bathroom set up - Single stack system. Sink, shower and bath all taken to the stack on the same waste pipe. Sink is about 5m away from the stack, shower about 4m and bath about 2.5m away. We have added an anti-vac trap to the sink and an AAV after the shower but nothing has solved the problem.
Am I right in thinking only solution is now to get the shower onto a seperate waste pipe into the stack (which will be a nightmare as our stack is inside the house and curved etc)?
Thanks for your help
KH

 

[hiretools]

Can't see why it won't drain.??? but if the drain pipes are not angled correctly to disperse of the waste, that would create a backflow towards the shower. Seems a bit odd, have u got the right trap on the shower waste ? let me know.

 

[easyt]

It might help to know - How high above (or below) the floor the bottom of the waste pipe is at entry to stack and how high above the floor the bottom of the shower tray is and the actual length of pipe run (4m?). I wonder what fall you have achieved.

 

[hiretools]

I was gooing to say that as well

 

[easyt]

t may be that there is little fall from the lowest point of the waste at the sink but it drains because there is a good vertical drop before it. Might be possible to increase the angle of attack to the outfall from the sink location. What fall should there be over 4m hiretools ? I Wonder.

It sounds as if when a good volume of water is released from the sink the vacuum effect pulls the water out of the shower after it. Might be as well to know what fall there is to the first connection (at the sink ?) from the shower.

Should also have asked what diameter waste at the various points.

 

[KJH]

Thanks for quick responses - the fall is vertical from the sink and then runs virtually at floor level until it meets the shower drain. It then travels a good 2 metres before a right angle turn and drops 30 cm to the stack over a 3 metre length (in the middle of this length, the bath waste joins). All pipes are 40mm.
Thks
KH

 

[easyt]

So how much fall is there? Sounds as i there is virtually no fall between basin and stack. Re-read the questions re shower base above floor etc. It sounds as if you have insufficient fall. Using the floor level as datum how high is shower base and how high is the main waste at bath and at outfall. I am confused because originally you seemed to say that shower had a 4m run to stack. It now sounds as if the shower drain has zero fall for 2m followed by a bend and then a 1 in 10 fall over 3m to the stack.

Just how high is the shower base. Sounds a very flat fall.

Easy T

 

[copperman111]

Hi,

Check building regs doc H
gives correct falls etc, difficult to diagnose without seeing it.

Was shower tray plumbed in properly? ie level all round
Ideally a seperate waste direct from shower would sort out your problem

Check all falls, make sure pipework not falling back to shower tray as
mentioned above.

If the correct falls and traps used then there should'nt be a problem its got to be the new tray installation somewhere i would have thought.(maybe)

 

[easyt]

If the stack is 4m from shower tray and all above floor then the shower should be at least 125mm above floor at a guess. Others on here would have a better idea. But if fall was 1 in 50 then in 4m 80mm fall and water trap at shower 50mm gives 130mm.

What have you got ??

(You can get shallower traps which would permit more fall. I think that you can get trap with 25mm water trap depth.

We need more info

Easy T

Edit: Should stick to a 50mm water trap if draining directly into a stack.

 

[KJH]

Hi
The shower tray is low profile but is on a leg set so maybe 15cm above floor level?

The shower trap came with the tray - it is one of those fast flow traps.

I think you may be right about the lack of fall. Because of the floor joists the first 2m from the shower are pretty much at floor level (along the top of the joists in a wall void) and then a bend and the pipe drops below the joists to meet the stack. Its just confusing why it drains after the sink creates a vacuum?

Thanks

 

[easyt]

Hi
:snip: Its just confusing why it drains after the sink creates a vacuum?

Thanks

Not really. When a sink full of water is released it fills the pipe bore and creates a vacuum that pulls the water from the shower. (Probably from the trap as well).