I have been using one of these for years. It only holds 4 liters at a time so probably only suitable for smaller aquarims, mine are 30L. There is a tap so you can adjust the speed of the drips, or even slow flow. I use it for water changes and acclimatising new shrimp. Made in USA www.zoomed.com so must be available there, and meant for reptiles?
The link is just so you can see the product from the UK place I get them.