Slope on bath drain pipe.

[Michael Chare]

I plan to install a new upstairs bathroom toilet, basin and bath. All three items will be on the same exterior wall. The basin is between the bath and the toilet.

If I connect the bath drain to the toilet soil drain pipe, outside just below the bath, a distance of about 8 foot, how much slope do I need?

Is it OK to connect the basin drain to the middle of the above pipe or should I have a separate connection to the soil pipe? The latter option would certainly prevent any water from the basin trying to enter the bath.

[John Rumm]

This has chapter and verse on all these subjects:

[polygonum]

If feasible, I would have separate connections to the soil pipe. I didn't and, whilst there is no real problem, I would not do so again. I feel it was a bit sloppy.

[The Natural Philosopher]

at least 1:100 1:60 is better, and more is OK but watch out for TOO big a flow actually sucking the U bend an trap dry. Or add an air admittance valve to it

If you can guarantee that only water is going down it and not solids that might collect it needs no slope at all. It can even go up - its just another U bend then :-)

[harry]

The optimum slope is 1:30. but not critical for wash basins. (Steeper rather than shallower) Separate connections are better. There's less chance of one trap "sucking the other out" Be sure to install cleaning points in the pipework so you can clear out any future blockages. Or use some compression fittings that can be parted for this purpose.

[Roger Mills]

Yes, but you can't! Bits of human hair inevitably get into bath and basin water - and these will collect at low points, and ultimately cause blockages. It's important to make sure that any long straight pipe has a downwards slope along its whole length, and doesn't have any dips in the middle.

[Michael Chare]

That is an idea I had not thought of!

Thanks for all the replies.