Modelling Capillary Filling - Sim Hydraulics/Fluids

Hi,

I'm using Simscape Fluids for the first time to model a fluid system that will be used in space (i.e. zero g). In one part of this system I have a capillary that will fill up to the top of the tube, then stop (surface tension prevents the fluid from exiting the tube), before an additional pressure causes the fluid to eject.

I'm modelling this as an ideal pressure source, with the net capillary pressure calculated using the Young-Laplace equation combined with a viscous term. I then am monitoring the height of the fluid in the capillary and the flow rate. Initially, I tried to model this simply using the Hydraulic Pipeline block; however the problem with this is that as soon as the pressure begins, there is flow downstream of the capillary - this should not be the case. I then replaced this with a tank (with dimensions of the capillary) that fills from a starting level of zero, as follows:

This works for when the capillary is filling up. However, the problem comes after this, when I apply the pressure to eject the fluid from the capillary - the tank goes to negative volume. This means that instead of drawing fluid from my reservoir upstream of the capillary, it is drawing it from this capillary 'tank', which is not realistic.

Are there any other ways I could model tube/pipe filling? Maybe have two parallel branches - one through the tank to fill it up, then one through a pipeline for after, with an idealised three port valve to choose which path the fluid follows?

(I'll also be adding complexity such as fluid inertia etc once I can work this out)