Bathroom drainage, divert into soil stack?

GeX · 8 Jun 2023 at 14:55

Currently, the toilet goes into the soil stack but the sink and bath go into another drain (old (Edwardian) house, mixed drainage).

It looks like this

The problem I'd like to fix is that when a full sink / bath is drained, it ends up flooding over the hopper that the pipes mix in

I have already bought a larger hopper and a new (black) down pipe but began wonder why this wasn't just connected to the soil stack in the first place. The main stack is cast iron but from the branch is plastic.

Is the drop not enough? Is there a risk that toilet waste would back up the sink/bath pipes if they were connected?

If there's a real reason why it can't be connected to the soil stack, what's the best way to stop the bath / sink from overspilling? Just a bigger, deeper hopper, a lid?

What would OcUK do? (Apart from replace it all in black pipe and repaint the soil stack as that's getting done regardless!).

The bath waste also carries the boiler condensate, if that's an issue for a cast soil stack or not, I don't know.

GeX · 8 Jun 2023 at 16:27

I don't think the hopper fills up and overflows, I think it's just the water flow into hitting the bottom / side and bouncing up. I looked into doing away with the hopper but due to the way drains are kept split on modern builds, there was nothing off the shelf to put a 40mm waste pipe into a 68mm rainwater pipe.

I'm not up for ripping out the soil stack and redoing that too, after having the house repointed and the roof / fascias / barge boards done I'm a bit skint!

GeX · 8 Jun 2023 at 21:50

The bit from the toilet to soil stack is plastic already. Presuming it's easy to tap into that then

GeX · 9 Jun 2023 at 16:04

The stack is vented.

The hopper is not overflowing, it's splashing over from high flow hitting at that angle

GeX · 9 Jun 2023 at 20:03

gingergundog said:
Personally I wouldn't bother getting involved with the stack, looks like unnecessary work/hassle. Looking at your pic I guess the easiest thing to do is fit a couple of 135 bends as already mentioned to try and direct the water into the downpipe rather than hitting the hopper. If you want to get really fussy about it put a section of 50mm pipe directly into the hopper then T those two pipes into it, seems a bit overkill though.

I’m not ripping any of the cast stack out, it already has plastic branched to the toilet. If the others can be joined, great. If not they’re staying at the hopper with some angles on the end!