Pan connector to soil pipe difficulties

[Bobbygee]

I’m trying to fit a WC Swan neck pan connector and the ribbed rubber section to soil pipe keeps riding up the straight part of the connector and not sealing to the soil pipe.
I’m fitting a back to the wall toilet and I have to fit the pan connector to the toilet first and lift the toilet with the connector spigot to the soil into the fixed soil pipe which is in the concrete floor to make the union between the toilet and soil pipe and the above happens every time. I’ve used plumbing silicone lubricant and the result is the same.
The swan neck is a new McAlpine. Can anyone advise please?

 

[denso13]

Are you fitting the ribbed part fully into the pipe first then inserting the rest of the connector?

I’ve used plumbing silicone lubricant

Use as little as possible, too much and the fittings can have a mind of their own.

 

[Bobbygee]

Thank you for the advice.
However every time I try to insert the ribbed seal it rides up the connector, it’s as if the ribbed seal is too big for the soil pipe which has a 100mm internal diameter.

 

[Bobbygee]

Are you advising that I insert the rubber seal into the soil pipe on its own and then insert the connector into the rubber seal?

 

[oldbutnotdead]

Have you got any cable ties and maybe some bits of batten (10mm or so thick)?
On the swan neck, above the ribbed rubber section, fix cable ties round the tube so they stop the rubber riding up. Try it
If that doesn't work, cut some short lengths of batten, cable tie them to the tube above the rubber, try again.
You may also have more luck if you have a friend so between the 2 of you you can lower the loo vertically onto the pipe (rather than hingeing it which is what I suspect you are doing cos it's easier)