Running guttering rainwater in same pipe as grey water from Garden room

[aido]

Hi,

We are building a garden room/office at the back of the garden. We are considering putting in a toilet, but there seems to be only one place to connect it and we are not sure its allowable.

Our house is a terrace house and the manhole is at the front of the house. So we need to connect to an existing pipe running under the house.

The Manhole has two inlet pipes in to it and one outlet to the main sewer. One of the inlet pipe is connected to the gutters at front of house discharging rainwater. While the other pipe discharges all grey and waste water from the house plus the rainwater from the gutter at the back of the house.

I know there are two drainage pipes running under the house (previous owners told me), one that takes all the toilet waste and one that takes the kitchen grey water. These two pipes join up under the house somewhere before they are discharged into the manhole. It looks like when the extension was added at the back by previous owners, the gutter water was discharged into a pipe running under the house which took the kitchen water (which then joins the waste) before dischargeing in to the main sewer.

Our builder suggested to connect the new office toilet to this pipe at the junction at the back of the house where the existing extension gutter connects to it. As this pipe eventually takes both forms of water to the manhole.

He also suggested instead of digging out a soak-way for the new office guttering, to also connect this water to the same pipe at the junction. But instead of two pipes to the junction from the office one for waste and one for rain water, he wants to connect them underground and run the one pipe up to the junction, as the toilet is expected to have very infrequent or little usage. Its not going to be a full time office.

To me this sounds like a short cut and possible illegal. Am I right?

Can you run waste in to a drainpipe which already has rainwater and waste running into it?

Can you add new rain water and Waste pipes to a drainpipe which which already has rainwater and waste running into it?

Is his suggestion of running rainwater and waste in the one pipe to a drainpipe which already has rainwater and waste running into it a complete bodge/illegal short cut?

 

[Ian H]

I'd do it, as long as it ends up in a sewer and not your local river.

It would be very unusual for the pipes to run under the house.

 

[aido]

Because its a terrace house it must have been the only way (rather than build a soakway) for the extension rainwater to get from back to front of house where mains are.

 

[Ian H]

If your house toilet and drain at the back you want to connect into both pass through the front manhole when you use them then I would connect to it if I were you.

 

[aido]

Thanks for taking the time to reply. Yes all drains pass through the front manhole. But they connect under the house and enter the front manhole from the same pipe. Would you run both the office rainwater and waste to the same pipe to the man hole??

 

[Ian H]

Yes, it will probably be a 4" clay pipe so will easily handle it.

 

[Hugh Jaleak]

Building Control will need to sign any drainage alteration off, I'd check with them they are happy with the proposals before doing too much more. All pipework will need to be accessible for rodding/jetting, especially as there's now a WC connected. Last thing you want is a blockage, then a flood from the WC when it rains.....