New Bath Install - Slow Drainage - Please help

[c0wb0y]

Hi there,

I was hoping you good folks could help with a issue I've encountered on a new 1700x700mm bathtub refit.

The issue is it takes forever to drain - I mean abnormally long @ +10 mins.

Starting at the compression end of the standard P trap, a 25cm length of waste pipe takes the flow 'back' towards the rear wall before elbowing into a 165cm length which terminates outside into a rainwater hopper. Looking at the waste pipework from a birds eye perspective, it would form a 'L' shape. I've used 40mm pipe and a compression elbow. The wash basin has its own waste and therefore the bath isn't connected to anything else apart from whats described above.

The 165cm length has a nice visible drop of approx 50mm. The shorter 25cm from P trap to elbow is flat and I can't see how to create a pitch on such a short run. The 'L' shape was necessary as the waste pipe can only be run BEHIND the bath legs.

Do you think its the 25cm flat run causing the issue? What can I do to fix that?

Being a complete newbie, the bathtub isn't perfectly level along the length - the spirit level is only slightly out at the rear. I can't see how that could cause this as I tested with the bath FULL. But can this be a cause too?

 

[muggles]

Waste pipe should fall at 44mm per metre ideally, so your 165cm run should have a fall of 73mm, although it should still drain reasonably well with a 50mm fall. Are you sure the initial short section isn't travelling slightly uphill? It would be best to try to get a proper fall on this too (11mm, ideally). How about posting a pic of your setup?

Also, do you have a standard plug and chain or a pop-up waste? If the latter, try taking the plug out to see whether that improves things

 

[c0wb0y]

Are you sure the initial short section isn't travelling slightly uphill? It would be best to try to get a proper fall on this too (11mm, ideally).

Good point but I wonder how this is possible without kinking the actual waste or the P trap i.e. How do you force a decline on such a short run?

The plug is a standard chain type.

I'll try to post a pic later today.

 

[Hugh Jaleak]

The elbow may not help matters, it will slow the flow down somewhat I'd think. Swept bends are better if possible, or 2 x 45° is you're having to use compression waste.

 

[hazetimesfive]

Silly question but is it a really cheap waste and does it have an overflow?

 

[Nige F]

Silly question but is it a really cheap waste and does it have an overflow?

I don't think it's silly - it could be a disc with a few holes in it

 

[75pete]

Would say, the bottom line is all about the fall to the soil pipe.

 

[hazetimesfive]

fall is fine from what I can see.

 

[c0wb0y]

Resolved - although not entirely happy. The problem turned out to be at the termination point where a 2nd elbow was fitted (a point i didn't mention in the op). It turns out water is very unforgiving when it comes to flow - it absolutelty must have a drop even on short spans.

Also, the 40mm waste pipe is so flimsy that it sags with the weight of the water! They don't make em like they used to. A block of wood was placed at the midspan to avoid this. The flow is only satisfactory but not perfect. Will be using solvent weld in the future for sure.

Thanks for all the suggestions and help.

 

[hazetimesfive]

I think you will find it is sagging due to the heat of the water, 40mm pipework should be clipped/supported every 500mm.

 

[dilalio]

Use solvent weld and rerun in 2" and replace plug & waste with a decent one - if you want to improve things!

 

[leakydave]

I bet it is push-fit pipe... total crap... sags and causes air locks and ultimately blockages