Garden office plumbing questions

[KnightWhoSaysNi]

I'm planning on building a garden office in place of the current shed. It will be at the back of the garden, ~ 40 metres from the house, and have a toilet, electric shower and washbasin.

From what I've gathered, for water supply I can use 25mm blue MDPE and this needs to be buried underground. Can I alternatively put it in a conduit and clip it to the fence?

As for waste water, the site is too far from the house so I'll need some kind of pump.

From what I've gathered so far, the most common solutions are:

1. A macerator (£200), but since their outlet pipes can only go up and then down and no other bends are allowed, I could only do it overground, e.g. clip it to the fence.
2. Macerator (£200), stainless steel dirty water pump with float switch (£100) and tank. Then run a small bore (40mm) pipe from the tank to the sewer.
3. Domestic pumping station which comprises a tank and pump (£700) - similar to 2., but more expensive and doesn't have a macerator, so a 65mm pipe would have to be used.
4. Domestic pumping station with an integrator macerator (£1800) - basically 2. but "all in one" and therefore more expensive.

Which would you recommend please?
I like 2. for the cost and versatility. Do I understand correctly that the pipe that comes out of the pump and goes to the sewer can have bends, and it can be either buried or above ground?
What kind and size of tank would work best with this setup?

 

[omega015]

Is the pipe from the tank going to be buried or run above ground? Also your going to need to apply for building regulations due to the toilet, shower and basin and probably electrics etc... So they will likely have a say in your options.

 

[KnightWhoSaysNi]

Is the pipe from the tank going to be buried or run above ground?

This is yet to be decided, but most likely buried.

 

[omega015]

If your likely to bury it then you might want to go that little extra and use some 110mm waste pipe, that way your less likely to get any blockages/issues with that.

 

[KnightWhoSaysNi]

If your likely to bury it then you might want to go that little extra and use some 110mm waste pipe, that way your less likely to get any blockages/issues with that.

From what I've read that's not needed at all when macerators are used. Their outlets are either 32mm or 40mm anyway. So having a larger-bore pipe between the tank and the sewer would offer no advantage?

 

[omega015]

Its not needed but if your going to the effort to dig a trench then I wouldn't want there to be a chance of a blockage somewhere in that bit of pipe. As for the pump/tank, that might not even be necessary if you can get a 1% fall on the waste pipe to the sewers (assuming you can if digging the trench).

As for the MDPE that can be ran above ground providing it complies with your local water regs. (e.g. protected from U/V, Undue Warming, Freezing, Potential contamination from the environment) however as your digging a trench anyway just lay it in that.

 

[just pumps]

1 & 2 are the cheap end of the range for a macerator to do what you require so expect problems in 24 - 36 months I would go for the pumping station with 2 macerating pumps working in duplex, run the pipe as per the MI`s and add a rodding eye so it can be jet washed through if required.

 

[KnightWhoSaysNi]

As for the pump/tank, that might not even be necessary if you can get a 1% fall on the waste pipe to the sewers (assuming you can if digging the trench).

The garden is 43 metre long. A 1% fall would be 430mm and I want the pipe to be a certain minimum depth where it goes in the ground to prevent damage.

I don't know how deep my sewer is, but I reckon it would have to be at least ~750mm deep for this to work. Are sewers normally that deep?

1 & 2 are the cheap end of the range for a macerator to do what you require so expect problems in 24 - 36 months I would go for the pumping station with 2 macerating pumps working in duplex, run the pipe as per the MI`s and add a rodding eye so it can be jet washed through if required.

A pumping station with 2 macerating pumps would be £4000 and that's too much for a £12K garden office.

The toilet / shower / washbasin will only be used one at a time.

If I use a 63mm pipe (or better yet, 110mm) with a pump I don't even need a macerator, so maybe that's the way to go.

 

[just pumps]

43m of 110mm @ 1%, not sure that`s even allowed tbh.

 

[John D v2.0]

Should be 1 in 40 really or 2.5%

 

[just pumps]

Yes of course it is, the 1% is for small bore stuff over a shorter distance, been a long day.

 

[KnightWhoSaysNi]

I've found a (single) macerator pumping station for £850. It has a 2" outlet. With that I wouldn't have to worry about the 1% or 2.5% sloping and I could use 50mm piping.

I'm wondering if I could use MDPE with that, and what type / colour for below ground and grey / black water?

 

[just pumps]

I've found a (single) macerator pumping station for £850. It has a 2" outlet. With that I wouldn't have to worry about the 1% or 2.5% sloping and I could use 50mm piping.

Oh dear lord I give up!
Goodnight all.