look how many beautiful problems I find you, you are not happy :D when you connect a valve to a storage-tank entity and change its type with shift-e, it completely empties the contents, if you move it with Even Pickier Dollies already changed everything is fine

"It's ALPHA! It's not finished, it's in Early access! You signed up for this when you bought the mod! Just ignore my giant piles of cash and keep reporting those bugs..."

I think what's going on is that the old valves were technically "storage-tank", so the toggle event would tell them to empty out and it would affect their internal buffer only. Whereas the new "valve" entity's fluidbox is connected with whatever is behind it.

They now have an exception and won't get emptied.