Waste pipe to main down pipe

[ad832]

hello every one, newby here, I've done a bit of DIY plumbing in the past (Trained Aircraft Engineer so use to hydraulic and pneumatic systems) and have a question relating to bathroom waste water going down the main down pipe.

At present the waste water pipe to the main down pipe runs above the floor with a step-down into the main down pipe. I want to run the pipe under the floor (to hide it) which would mean it would be a straight run into the down pipe - is this acceptable ( of course the shower and sink will be fitted with a trap)

Many thanks AD

 

[townfanjon]

Straight run definitely not mate

 

[ad832]

Jon Thanks for the reply, I'll look to see if i can drop it where it goes into the main down pipe

 

[PlumbBobBob]

which way do the joists run? i'm guessing perpendicular to the pipe.

 

[joni os]

Straight run definitely not mate

Why?
Provided no conflict with other connections and cross flow not an issue. Old copper wastes commonly run straight into cast soil/vent, via brass boss, with no problem after 50+ years. If joists perpendicular to run, that's a different issue.

 

[townfanjon]

By memory joni , isnt it 18 mm per meter fall on a 110 pipe . I wouldnt run one straight , anywhere .

 

[joni os]

Maybe misunderstanding. My interpretation of straight:- shortest distance between two points.
Not necessary to be horizontal.
Fall on 40mm shower waste pipe :- between 18mm and 90mm/ metre run.( Length not exceeding 3 metres, recommended but not mandatory).

 

[ad832]

I'll have another look and see what i can do