Universal Water Diverter Kit

You could locate/buy a longer hose of same diameter, Or, fashion an adapter to a piece of garden hose. Even using some duct tape or Gorilla tape to attach the garden hose would work

You set this up PARALLEL to the barrel entry point. When the barrel is full, the water rises over the top of the tube. When the tube is under water, and parallel to the diverter, there is no longer a place for the water to go so it backs up higher in the diverter. The middle of the diverter has a giant round hole in it - it has a lip whch is higher than the tube-hole, but lower than the drainpipe / rectangular outside lip. This allows water to pour down the middle a) when the tube is 'overflowed,' b) before it is high enough to escape the rectangular downspout.

The hose must be exactly horizontal. I installed one correctly level and rain barrel filled up. The other one the rain barrel was millimeters higher and would not fill

Men is small like 3/4 inch

Outer Diameter of tube is 20mm or 13/16 inch

FWIW I installed this and it filled a 40 g barrel in very little time. My fears about the tiny tube were misplaced.

I got it few years ago , it is very easy to install and work great . Only problem is buying the replacement parts ever I send the message to the company but no reply.

DO NOT JUST PULL OUT THE TUBE There is no option to comment on other answers, but look at the picture: The hole the tube is in is lower than the overflow that sends water back down the downspout (by design). If you pull the tube out of the hole, the water cannot overflow the diverter center piece because the hole you just left will allow the water to escape and run down the outside of the unit and downspout. All the other answers are ok - from tiling the hose up to plugging the hole - the key is the water won't go down the downspout until it meets resistance / can rise higher than the hole.

No, this kit is not intended for use with a round downspout.

very easy to install