Waste outlet for wash basin -newbie advice please

[Flinstone]

Hi.

I had a flood from our upstairs bathroom after a compression bend came off a 32mm waste outlet pipe from a wash basin, caused when using a pump-type sink unblocker.

The previous installer had not made a particularly neat job of the layout nor with the water pipework either. I have tidied up the water pipes and hidden them inside the basin pedestal and would now like to do the same with the waste outlet by drilling a new hole through the floorboards in line with the new slimline pedestal waste trap I have bought.

I would like to replace the existing compression fittings with solvent pipe & fittings (2 bends and a straight coupler) - so now to the point of my request for advice:-

1. Are compression fittings designed to fit both standard pipe AND solvent pipe (having a larger O/D)? Basically, is it standard practice to connect solvent pipe to basin traps using their compression fitting? I know Marley describe them as Multifit, but is it true?

2. Because the longest pipe section is 1500mm (3000mm o'all run - see item 3) am I correct to understand that there is no need for an expansion fitting?

3. The vertical section of pipe from the waste trap (500mm incl. trap) will go down under the floorboards and then run horizontally (bend #1) for 1500mm before turning (bend #2) on another 1000mm horizontal pipe, where it will finally meet the waste from the bath to the hopper outside (a very short distance). Should both bends be 90° bends? I ask because I see also 88½° bends from Marley (are these also called 92½° bends elsewhere?). Are they solely for having a wider sweep or are they to do with aiding a fall off? I appreciate I need a fall and wonder if 90° bends would be wrong. My argument for needing them is that I mentioned the pipework is travelling under floorboards. If I use a 90° bend (#1) at the point of entry under the boards (highest part of the fall), the smaller bend radius will aid greatly in keeping the fall within limits. If I use the larger 88½° bend then the pipe end will have lowered by at least 10mm which concerns me.

Thanks in advance & kind regards

 

[kirkgas]

McAlpine multifit does what is says on the tin every time, given the length of the pipe run i would suggest using 38mm rather than 32mm to minimise choking problems

 

[swidders]

If you can get 50mm waste pipe under the floorboards (32mm rom trap down to this), then so much the better long term.

The 90 bends you refer to are of two types (and of the same angle) - swept and knuckle, and their names are self explanatory - any plumbers merchant will advise.

 

[Flinstone]

Thanks for comments.

I don't think I can increase pipe size from 32 because there is already a notch on top of 3x joists where the 1000mm section crosses on top of them.

@swidders:
Sorry but still confused about the basic reason for 88½°, 92½° bends etc. If they are 90 bends and of the same angle, why are they advertised in varying degrees?

I appreciate the obvious reason for a swept bend (which I had thought were all descibed as non-90 bends). And what typical application is a knuckle joint used for in a waste pipe if it aids blocking if used?

Sorry if I seem dumb about this, maybe I'm thinking too hard perhaps!

Cheers

 

[kirkgas]

under "normal" use a couple of knuckle bends are fine, and if above floor can be accessed if required, when you move to under floor and longer runs you could have a problem, another option is to use 2 x 45 degree bends together as a 90 to help with the flow, (ok if you are putting them horizontally as vertically they add a fair bit to the height).