basin waste comes up in bath

[anotherbillalready]

Hi,
Help, please.

When I empty a full basin, waste water comes up in the bath.

How could I cure this?

I've lived with it for a while, but it's annoying & I'd like to know a solution.

I had a new basin plumbed in ("professionally"), which followed the existing link to the bath waste (which in turn flows to WC back, on to stack)..

It's a 1-level apartment, the set-up is like this:
Basin > u-trap (new, plastic 30/40 mm ish )

- V vertical drop 2 ft or so (old, metal 1½ inch)
.

> horizontal (or thereabouts) to a main stack
> it passes the bath small u-trap, about a yard on
> then it passes the back of the WC (usual U-trap), another 5 or 6 feet
> finally to stack another 5 or 6 feet . . . .
--

--

(2nd floor of 10 storeys, It's a 4inch stack - I dunno, '50s I guess...
which serves bathrooms & WCs. )

I assume the drop on the level is best practice, 2 degree or so, but it may be a flat.

So far as I know, the drains & stack are clear.

The original drainage, of good standard '50s, copper 1½ inch, incorporated an air-vent between the basin & bath, now blocked off.

Air-vents were standard back then, you still see them outside old houses in town. Personally I think they are superior to valves & such, which are often noisy).
The vent may have acted as a sump, I suppose, but would be a bit small for that.

The plumbers blocked the vent off, &/but did not fit a valve (probably my objection to the noise they make, & it might be OK anyway).

Any suggestions?

 

[tommyl18]

youve got a partial blockage either in the stack or between the stack and the bath

 

[anotherbillalready]

Thanks, tommyl18, that could be true, I don't know.

How would I check that, without the expense of actually pressure flushing the stack?

I don't seem to have any problem with the WC flush, it flows easily.

I've had a snake-rod along from the basin to the WC, so I reckon that's OK.

I just wonder if there's a way of re-configuring the pipework to help?

Maybe it's an air flow thing.

My easiest solution would be just to restrict the basin outflow (if leave the plug half-in, that works), but it seems an unsatisfactory solution.

Any further ideas?

 

[Nige F]

Small u trap on the bath - change for a deep seal one or a Hep V.O waste valve - simples

 

[anotherbillalready]

Thanx, NigeF

A slight extra difficulty is the lack of clearance between the bath waste & the concrete floor (it needs a very small &/or flexible plumber to get in there! The Victorians would have had no problem ;-D ).

I think the essential problem is that the water level 'in bath' tends to equalise with the water level in the basin, a couple of feet higher, so I'm unsure how a deeper trap might work (apart from the limited height available ).

I can imagine that the extra weight of water in a bigger trap might hold the passing inflow back to some degree, but not all that much. It's a question of whether the inertia would be enough for the length of time the basin takes to empty.

I could build something almost sump-like in the few inches available. Do you reckon that would work? Maybe that was how the earlier air-vent functioned.

I've just spent a frustrating few minutes trying to ascertain the depth of a Hep valve, whether it can be fitted sideways (regs?), and what height one needs above to open the valve - things Hepwort's site clearly considers to be unimportant or too obvious to note..

Also, it seems primarily to be a gas trap, I wonder how it copes with back water pressure?