38mm European waste pipe to 40mm UK compression waste fitting

[Ian101]

What's the best way to ensure a watertight fit connecting a 38mm European / continental waste pipe to a 40mm UK compression waste fitting without using a 38mm to 40mm adaptor prior?
The reason not to use an adaptor is because there's no space.
Note, a 40mm compression fitting on a 38mm pipe will hold however the joint won't be as tight, both mechanically and water pressure. Hopefully there is a way to improve the seal - a specific sealant, tape, compound?
Pipe and fittings are polypropylene.

 

[rpm]

The adaptor ring takes very little room to fit and what you are asking for is a bodge. Change the waste instead?

 

[snowhead]

Are you joining 38mm directly into a 40mm elbow so no room for this as well?

https://www.NoLinkingToThis/p/mcalp...VmpntCh1iBQrnEAQYBCABEgLRjvD_BwE&gclsrc=aw.ds

 

[Ian101]

It's a 40mm compression coming vertically out the floor solvent welded to the waste pipe below the fixed floor - It's situated at floor level. It connects to a 38mm flexible waste below a shower. The area below the shower base does not provide much room. A 38mm male to 40mm male tight elbow long enough to compression join on both sides would work but the fittings does not exist (I think).