Condensate drain for a ventilation unit

[JT101]

I have two small ventilation heat recovery units. Only large enough to extract and supply to one room each per unit

I have to fit a condensate trap to the underside of the unit, and then connect into the waste (one SVP and one RWP downpipe).

I don't know why this is still such a specialist subject, and not much info on the web, but I can't find a standard practice for this.

The slope is short (600mm) and horizontal with say 5 degrees

Looks like some people just use lots of 90 degree overflow pipe 21.5mm e.g. http://mindtomachine.blogspot.co.uk/2010/08/new-ac-condesate-traps.html

But others use products like the HEPVo or EZ trap. Some use flexible hose and others not.

So have inspection caps at the top and others not.

A few questions then


1) Can I just make my own trap out of elbows and overflow pipe 21.5mm or is there a better way

2) what dimensions should the U-bend be?

3) Can I go into the rainwater downpipe with one of them, or is that considered mixing surface water with waste water?

Thanks