Best way to connect trap to floorstanding bath

[Milleniumaire]

Today I picked up a McAlpine trap and a Flexcon6, which I thought would help me plumb in my floorstanding bath, but it hasn't worked as expected.

When I screw the trap to the waste on the bath, the trap is within the void underneath the bath. I bought the flexcon6 as I thought one end would screw onto the waste and the other end onto the trap and this would give some flexibility to fit the trap with the bath sitting on blocks, then remove the blocks to allow the trap to sit below the floor surface, in a hole cut through the floor under the bath.

It hasn't worked because the flexcon6 isn't designed to screw onto a bath waste. Doh!

Here's a photo of the issue:

20200605_195750

• Milleniumaire
• 5 Jun 2020

It looks like the screw fitting is about 7cm below the bath base, so I think I need to use something to extend the trap to fit outside of the bath base (which is why I originally purchased the flexcon6).

I'm wondering if the McAlpine Flexcon9 is what I need? This has a BSP coupling nut at one end (connect to waste) and a BSP male thread at the other (connect trap to it?). I could then simply use a 40mm pipe and nut to connect to the output end of the trap. The flexibility of the flexon9 allows me to raise the bath to screw it to the underside before lowering it. I guess the only potential issue is that if it is too long I may not get the fall on the waste pipe!

Alternatively, I wondered if this BSP female to BSP male coupling might be the right thing to use to allow the trap to be fitted lower. I suspect the 3" version would be required. I'm assuming the waste pipe connect to the trap might need a flexible fitting to allow some movement due to the bath being raised, then lowered?

I've just come across this adjustable trap, which may also work as it allows the trap to be lowered. Wish I'd seen this before! I guess I would still need to incorporate a short piece of flexible pipe in the waste run to the outside wall, which would allow the trap to be screwed into the waste while the bath was raised, and then lowered into place? The run from the bath waste to the outside wall is 48cm so I guess even plastic pipe would allow a bit of movement, but I'm not sure it would be enough (depending on the diameter of the hole going through the outside wall).

 

[Ian H]

I used one of those flexis on mine, couple of pics on here:

https://www.diynot.com/diy/threads/fitting-a-free-standing-bath.517356/

 

[terryplumb]

Flexcon 6 has a spigot on one end and should connect straight into the trap outlets compression fitting ??

 

[Madrab]

yup +1, then the compression end is used to connect to the 1 1/2" waste pipe run??

 

[denso13]

This has a BSP coupling nut at one end (connect to waste) and a BSP male thread at the other (connect trap to it?).

No, this is a trap extension https://www.toolstation.com/mcalpine-bsp-coupling-3-long/p19305. The Flexcon won't replace that but will fit on the trap outlet

 

[Milleniumaire]

I used one of those flexis on mine, couple of pics on here:

https://www.diynot.com/diy/threads/fitting-a-free-standing-bath.517356/

Thanks for the link. I see you eventually used a piece of flexible waste pipe connected to a P trap. As well as requiring the flexibility of the waste pipe to allow me to raise the bath to fit the trap, then lower it into place, I also have the complication that the waste fitting on the bath is high up and so the trap I have purchased needs to be lowered by installing something between the bath waste and the trap. You don't appear to have had this issue although it's difficult to see exactly what the other end of the flexible pipe is connected to as it appears to bend downwards. I would have expected your waste pipe to run horizontally between or through the joists to the outside wall, so not sure how the end of the flexible pipe is connected to your waste pipe, possibly using an elbow?

 

[denso13]

needs to be lowered by installing something between the bath waste and the trap.

https://www.toolstation.com/mcalpine-bsp-coupling-3-long/p19305

 

[Milleniumaire]

Flexcon 6 has a spigot on one end and should connect straight into the trap outlets compression fitting ??

No, this is a trap extension https://www.toolstation.com/mcalpine-bsp-coupling-3-long/p19305. The Flexcon won't replace that but will fit on the trap outlet

Thanks guys. I think maybe I didn't explain my issue very well.

I know the flexcon6 can be connected to the "outlet" from the trap using the spigot, however, I actually purchased this to fix between the bath waste and the trap and clearly it isn't designed to do that.

In my earlier link I identified what I think is the correct item to "extend" the bath trap so it sits lower down i.e. further away from the bath to get around the problem that I currently have in that if I screw the trap onto the bath waste, the outlet is "within" the body of the bath and I can't connect any pipe to it, as you can see from my original photo.

Having done more research I've also realised that although I purchased a bath trap that was identical to the old one I believe this has a 50mm depth of seal and according to building regs the trap should have a 75mm depth of seal when the waste pipe is connected directly to the soil stack? Given the house is 22 years old and the old bath waste worked okay all that time, I don't think it would be a big deal to use the 50mm depth seal trap that I've already purchased. I will be re-routing a brand new waste run due to the need to hide the waste between the joists, so not sure if that makes a difference.

To, to clarify, I have two issues:
1. The void under the bath makes it difficult to fit a trap directly onto the bath waste as the outlet from the trap is then within the bath void and using the 50mm depth of seal trap I have, the outlet is also very close to the edges of the bath (see my original photo).
2. I need to be able to lift the bath to attach the trap to the waste, then lower it down. This therefore requires some flexibility in the waste pipes.

To meet building regs, I guess I should get a 75mm depth of seal trap and this looks to be a P type trap. McAlpine do the adjustable P trap but all the reviews I've read on Screwfix suggest this is designed to be used for a sink. I'm not sure of any reason why it shouldn't be used for a bath.

 

[Milleniumaire]

So, having examined the bath and trap again and using a little brain power, I think I may have figured out what I need to do. What I wasn't taking into consideration was the ability to redirect the trap outlet and now that I've realised that it seems that the bath trap can sit within the void underneath the bath and I can use a flexible fitting to connect the outlet to the waste pipes under the floor. Unfortunately, the trap does protrude beyond the bottom of the bath, so I would probably have to cut a large area of the floor board to accommodate it and the waste pipe!

As I have already purchased the flexcon6, I could use this, but think I will need an additional elbow under the floor:

20200606_101414

• Milleniumaire
• 6 Jun 2020

Alternatively, I could purchase another flexcon2 (which I have used for the shower) and this would allow two bends, although it does require quite a bit of force to keep the bends in position:

20200606_102418

• Milleniumaire
• 6 Jun 2020

This still doesn't really address the issue of the seal depth: 50mm or 75mm, but I'm less concerned about that or should I be? I assume the larger the seal depth, the less chance there is of syphoning? If syphoning were to be an issue, I could always replace the trap with a similar shaped anti-syphon version!

 

[Milleniumaire]

Having consider my previous suggestion further, I'm not totally happy with it as it requires a lot of flooring to be chopped away to allow for the trap AND the flexible pipe.

So, I'm back to my originally idea about using a flexible BSP connector that will allow the trap to be fitted under the floorboards.

The McAlpine flexcon9 is pretty much what I need, however it is just too long, with a minimum length of 26cm. It would result in the trap being positioned very low down in the floor and I think I would struggle to get the required drop to the outside wall!

So, given that the McAlpine flexcon6 is pretty much spot on for length and I have already purchased one of these I've realised I can buy a couple of adaptors to allow one end to be connected to the waste and the other end to the trap. This would give the following "sandwhich":

Bath Waste
|
McAlpine T29-LN - Straight Connector multifit x BSP coupling nut 40mm
|
McAlpine Flexcon6 - Universal x Plain Spigot
|
McAlpine T31M - Straight Connector BSP Male x Universal
|
McAlpine SM10 - 50mm Seal Bath Trap with Cleaning Eye

The trap and the run to the outside would be fitted underneath the floorboards, with a piece of wood underneath the trap to hold it at the correct height, so it doesn't push down when the bath is lowered and the flexcon6 compressed!

The flexcon6 and the BSP adaptors give me the flexibility to raise the bath, connect the extended flexcon6 to the waste (via the T29-LN adaptor) and then lower the bath, which will compress the flexcon6. The trap and waste pipe under the floor shouldn't move at all! If I make the hole in the floor larger than it needs to be, it would allow the trap to be removed/replaced from above if this is ever necessary.

I would appreciate some confirmation that these products will do what I require as there appear to be a lot of very similar products sold by McAlpine!

 

[Madrab]

What trap are you wanting to use? I wouldn't use the bath trap you have fitted to the bath at the moment, it isn't really designed to be a remote trap, it's designed to directly connect to a waste outlet unless you can securely fix it to a joist or baton, alternatively a running trap or waterless trap could be used but again whatever is chosen it really should be securely fixed so it can't move. The other consideration is access - the more connections/fittings that are incorporated means more places for it to spring a leak, so rule of thumb is keep it as simple as possible and factor in access as part of the design for servicing.

As far as a 50mm or a 75mm seal is concerned then you don't need to be overly worried about that. The greater the seal the less chance of it being pulled but a 50mm seal at a min should be fine.

You can't really get much better than McAlpine for waste fittings.

 

[Milleniumaire]

What trap are you wanting to use? I wouldn't use the bath trap you have fitted to the bath at the moment, it isn't really designed to be a remote trap, it's designed to directly connect to a waste outlet unless you can securely fix it to a joist or baton, alternatively a running trap or waterless trap could be used but again whatever is chosen it really should be securely fixed so it can't move. The other consideration is access - the more connections/fittings that are incorporated means more places for it to spring a leak, so rule of thumb is keep it as simple as possible and factor in access as part of the design for servicing.

As far as a 50mm or a 75mm seal is concerned then you don't need to be overly worried about that. The greater the seal the less chance of it being pulled but a 50mm seal at a min should be fine.

You can't really get much better than McAlpine for waste fittings.

Thanks for the feedback Rob.

I was planning to use the trap shown in the photo as it is a brand new McAlpine trap I have purchased for the job. I got this one as it is similar to the old bath trap and I didn't know any better!

A number of points you have raised are new to me, such as the concept of a "remote trap" and securely fitting a trap to a joist or baton, probably because I've only done plumbing work in my own homes.

Regarding a "remote trap", I assume this means that the trap isn't directly connected to the waste, but somewhere in the pipe run, so although in my case, the trap would be in the floor space directly below the bath, it is still regarded as a remote trap as it has pipes on either side?

I've been looking at a lot of traps on the McAlpine website and I've not noticed any of them having design features to "secure" them. Are there traps that are designed to be used remotely with fixings to secure them? I guess in my situation, because there is flexible pipe to the trap and solid pipe after the trap, you are saying the trap "could" move with the force of the bath water? The trap will actually be situated close to a joist, so in theory I could fix it, but not sure how this would be done and why this particular trap would be more difficult to secure than other traps? I was planning to sit the trap on a wooden "ledge", but could expand this to box it in on three sides as well, so that it can't move horizontally or vertically? Obviously, the 4th side would have the outlet pipe connected, which will run through the outside wall.

Access shouldn't be a huge problem as I can cut a large hole in the floor directly under the waste of the bath, which would allow access to the trap, but obviously the bath would need to be moved to get access. I expect it will be stuck to the tiles using silicon around the four feet to avoid movement. Alternatively (thinking as I go here), I could glue some batons at 4 "corners" so that the bath can't be moved in any direction. This would make it easier to lift the bath without trying to break the silicon seal on the bath feet, which might be difficult.

I agree regarding the number of connections, but I'm struggling to come up with an alternative solution.

 

[Milleniumaire]

.... just re-read your post Rob and see you mention a "running trap". I see what you mean now. This is designed to be in the pipe run, not directly connected to the bath, so I could potentially use this in place of my existing trap. I would then only require the T29-LN adaptor to attach the flexon6 to the bath waste, with the other end going to an elbow and then into a trap. This would make the trap access more difficult as it wouldn't be directly below the bath.

I need to use "some" flexible pipe to allow me to have the bath lifted when making connections and then lowered into place.

 

[denso13]

I know the flexcon6 can be connected to the "outlet" from the trap using the spigot, however, I actually purchased this to fix between the bath waste and the trap and clearly it isn't designed to do that.

I understood that which is why I gave you a link to the correct one, twice. https://www.toolstation.com/mcalpine-bsp-coupling-3-long/p19305 fits between the bath and trap to "lower" the trap.

 

[Madrab]

Regarding a "remote trap", I assume this means that the trap isn't directly connected to the waste, but somewhere in the pipe run, so although in my case, the trap would be in the floor space directly below the bath, it is still regarded as a remote trap as it has pipes on either side?

Yes, exactly that.

Most remote traps would be secured by being part of the rigid pipe run and that would in turn be clipped properly therefore little danger of the pipe sagging or a trap moving. You plan to use flexible connectors etc therefore there is potential for the trap to move, not something you want. As far as securing any trap you would be using then you can use a few different methods, pipe clips/galvy banding, etc.

A waterless trap may be consideration for you as it can be fitted 'in line' but again you would want it/the pipe either side securely clipped