To trap or not to trap?

[Welderpaul]

If I used something like this to connect bath and sink waste to external 110mm drainage, would the external drain need to be trapped?
Presumably the bath/sink trap would be enough?

How about RWPs? I'm looking to use something like this? Would it need to be trapped?

 

[Agroshield]

...would the external drain need to be trapped?
Presumably the bath/sink trap would be enough?

How about RWPs?

External drain, no. That is the whole idea of the adaptor - so there is an airtight (smell-proof) seal between small and large pipes.
Bath or sink trap is enough. Just make sure there is no suction in the foul drain to empty the trap.

RWP depends on if it is a combined system (foul and surface water together) or rainwater (surface water) only.

You might get away with a RWP into a foul without a trap as long as the gutter connected to it was 1m above any window, but RWP joints don't have rubber gaskets so have potential for smell to escape.

 

[Welderpaul]

Right thank you.

It is a combined system.
Gutter is more or less 1m above windows, and yes, with unsealed joints in the RWP

 

[gaz1]

you will need anti vac traps on your wastes otherwise it will leave you with drain fumes from the drain

it does suck on the water within the traps when you release the water from the plugs