You do have to prime it to get the tube filled with soap. If it isn't completely filling with soap, you could have a lot of air pumping going. Check your line. The backflow valve needs to be going in the right direction, so make sure you put the right end in the soap. Also, if you are getting any air leaks, the line may not be staying filled with soap. Check that the ends are all tightly fitted and there are no signs of leakage.

Some folks thin their soap with water, but I have never had to do that.

Mine are attached to Graff dispensers.

I had similar issues when we installed ours. Check a couple of obvious things: make sure the tube isn't being pinched, make sure it is snug on both ends. Our tube on one sink needed to be rerouted because a drawer (it's the stages sink one) was pushing the air switch tube into the Never MT tube and causing it to be a little squished. Wasn't obvious when we checked it because, the drawer was pulled out when we looked and all was fine. Kind of like the naughty girl pulling another girls hair when no one is looking....

Just keep pumping it. Ours seems to have softened up a bit and now works much better.

We have the elkay dispenser, not a grohe.

Could be your soap dispenser too. I had an issue and it turns out I had a fault pump for the dispenser. This was a brand new unit. Got a new one and no issues. Need to get a new one though for our new house.

Thanks everyone! I don't think it is the dispenser. It has worked just fine for the last few months with the bottle that came with it. I will try to follow your suggestions and get back to you with results.