Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Home Depot has a pretty good selection.
The thin wall tubing tends to collapse, so get the thicker walled material.
1/4" is about the size of air tubing. Slow flow, but easy to clog. (just use air tubing, no need to buy this size)
3/8" is much better.
1/2" is OK (does not clog much), but can get going too fast for a small tank, you may have to slow the flow by either pinching off the tubing a bit by hand after it leaves the tank, or else raise the bucket. If you need to moderate the flow by hand, the thin wall tubing is much easier to pinch off.