Plumbing / Building Question - Add garage sink

[lookitsjonno]

I want to add a small sink into our garage for hand washing. My plan for fresh water is to T off an outside tap which should be easy enough, but i'm struggling with waste. Thankfully the waste inspection chamber is only about 3 meters away. How can I run my waste into the chamber (image below)? Can I just drill a hole through the black plastic at the side a couple of feet down and slope a 1.5inch waste pipe into it?

 

[pp111]

Erm, yes you can. You want the pipe to drop down in to the chamber to guide the water to the right place and the top of the pipe should be fully vented ( so it doesn't create back suction when the water falls ). It's called a dropper pipe. However, you are not allowed to modify systems without approval so I would keep it quiet and remove it should you ever move.

 

[2004typer]

Does the garage have any rainwater pipes on?

Obviously a no no to boss into if going into a surface water system only or a soakaway (if so do not do this) - but on the off chance all of your sewers are combined where both foul and surface water go into the exact same sewer it would be a lot easier than connecting into the chamber below ground, and a lot easier to remove afterwards.

If you do connect into the chamber you need to make sure the aperture you make is water tight as well in case the sewer ever blocks, you don't want foul water leaching out into the surrounding ground.

 

[lookitsjonno]

Thanks guys opted to do the job properly and hook it into a blank on the chamber directly. Killed me yesterday digging the 1 meter deep hole mind.

 

[2004typer]

Thanks guys opted to do the job properly and hook it into a blank on the chamber directly. Killed me yesterday digging the 1 meter deep hole mind.

Good effort and definitely the best way - don't like it when holes are made in the side of pre-formed PPIC chambers, they tend to lose their integrity and water tightness.

The connecting pipe down your trench will have a steep fall, but if it's only a sink it won't matter at all (only really becomes absolutely crucial when a toilet is connected to ensure solid waste and water travel along together rather than separate).

You could put a trapped gulley alongside the garage wall now and then connect the sink through the grate (make sure it goes through the grate cover), alternatively you could just stop the 100mm pipe at ground level with a bossed stop end for the reduced diameter sink waste.

When you lay the pipe, bed and cover this in some pea gravel, but if there are any sections with a depth less than 450mm to the crown of the pipe chuck some semi dry mix concrete over (but not over the pipe joints - leave a separation layer there using a bit of flexcell or similar). The 450mm depth is to protect from damage (i.e. somebody driving a pitchfork or similar, for example, into the pipe).

 

[lookitsjonno]

Thanks for that, did exactly as you said and laid in pea shingle above and below. Just finished filling it back up. Pipe work fought me every step of the way so ended up with an adjustable jobby. Queue several trips to Toolstation and lots of swearing I'm pretty pleased with the result. We plan to patio the area for an outdoor kitchen later in the year but most from halfway onwards is 450mm or deeper.