Since the original had a few sharp corners and edges that were a bit tricky to clean and got some dirt and alge stuck in, i've changed the geometry slightly
if you use a silicone tube, it does not really matter - i use a 1,8 inner x 2,6 mm outer diameter tube, that works quite nice
this one on amazon: https://www.amazon.de/gp/product/B092HZPKCY/?tag=rebellat-21