I just bought a bottle trap but I'm unsure about the connection. One side is standard push fit - you can see this in the image it is on the far side with the black ring around it. Each of the other three accept a 110mm pipe inside of it, but there is no rubber seal.
Ah I think that the idea is that the hole is drilled and then a pipe is inserted and it overhangs inside the chamber so that water falls directly into the bottle. If anyone has seen one before and could confirm I'd still appreciate the confirmation!:)
Normally it is solvent welded but never seen anyone do it, most guys just push it home. If doing a lot, solvent weld would be my choice, also easy to push on if in brickwork but for one off flexi will do.