Replacing cast iron hopper and downpipe with plastic??

[Sleebagz]

Hi I'm looking for some advice on replacing a cast iron hopper and downspout with plastic.

The hopper takes 3 waste water pipes from the bathroom and one gutter from a flat roof, I was intending just to wire brush and paint as with the rest of the metal guttering I have but on closer inspection this small section is in a lot worse condition and the hopper is VERY thin and rusted.

I'm wondering if I should:

A) Buy a new plastic hopper and cut the old metal one out, somehow hoping the outlet hole for the plastic hopper will match up perfectly to the metal downpipes.

B) Remove the whole lot, cutting the metal downpipe off at the base and running a new plastic hopper and spout down into the metal that'll be left as it's cemented into the clay drain.

I've tried to measure the diameter of the downpipes but it's difficult without having a cross section - I'm worried if I cut off at the base the new plastic 68mm won't fit inside the old metal part at the bottom and I won't have a water tight seal.

Will a 68mm down pipe connector allow the plastic pipe to fit inside the metal one?

Any help or advice greatly appreciated!

Photos below explain what I'm on about....

 

[Carlos74]

I went with option C recently, I bought a reclaimed victorian hopper of ebay to replace a cracked one I had.

 

[Nige F]

Having looked @ the setup / sizes etc. I agree with Carlos.

 

[Tigercubrider]

Use a bit of string to measure the circumference - then the diameter can be worked out.
Or buy a cheap set of caliper/vernier gauges

 

[vinn]

Sleebagz,

Is the down pipe actually catching the gulley through a side inlet or going to a separate drainage?
Run a water test from the hopper and watch if the water ends up in the gulley.

You seem to have a raised gulley surround that's been constructed to deal with the raised yard surface.
Chip off the smeared on sand & cement above the gulley proper to release the down pipe fitting. Dont attempt to cut & force plastic pipe into it. It will be perished and possibly leaking.
Now remove the down pipe and hopper.
Replace the hopper & d/p in CI or plastic. You will have to 45 degree out just above the gulley.
Replace the broken gulley grid.
Patch the surround with mortar.



How will knowing the OD give the ID of an old CI pipe? And anyway, if you need the OD all you have to do is measure across.

There isn't an option C?

 

[Sleebagz]

Is the down pipe actually catching the gulley through a side inlet or going to a separate drainage?
Run a water test from the hopper and watch if the water ends up in the gulley.

Yes the water enters the clay gulley from an inlet at the back.

Why can't I just cut the metal pipe off at the bottom and try and get some sort of adaptor for the new plastic down pipe to run it straight into what will be left? I've seen old metal pipes cut off at ground level with a new plastic one going into it before, is this not a solution?

Surely if the new plastic pipe has a tight(ish) fit inside the old metal one gravity will be enough to prevent water spilling out?

I'm tempted just to wire brush the lot and paint it, see if I can get a few more years out of it.....