Just to be clear I AM NOT TAKING CREDIT FOR THE IDEA and props go to UNKNOWN for his write up for inspiring me (and to his inspirations) all i'm doing is letting people know what materials I use and how I put these together for 20mm Conduit.
First of all what you need:
a 32-25mm conduit bush (available from bunnings).
a 25-20mm conduit bush (available from bunnings).
a washer from a 3/4BSP female washer seal gas connector (available from gas fitting / plumbing shops or PM me).
some rubber sheeting (I just use some wheelbarrow inner tube).
a stapler with staples.
a marker pen.
and some 16mm conduit to trace around.
Step 1: trace a circle around the 16mm conduit onto the rubber sheet, and then square it up from half way.
Step 2: cut out your 'flap', make sure you have excess to the square side - this can be trimmed later.
Step 3: place your flap on your washer andmake sure the flap just covers the hole.
Step 4: staple it in place (if you're using inner tube make sure the shiny side is towards the washer) make sure the it is stapled flap up.
Step 5: place the washer/flap assembly into the 32-25mm conduit bush(make sure the flap is on the inside of the bush)
Step 6: push the 25-20mm conduit bush into the 32-25mm bush and wedge the washer in place - don't push too hard as then the washer will bulge
and then you're done - just put it on a 20mm RSCB or hopper and you're good to go