A foaming soap dispenser
We bought one of these commercial soap dispensers because we ran out quickly with 7 people washing their hands. So this was the least industrial I could find.
It came with a box of refills that were quite expensive but I hoped I'd be able to refill. I scarified many empty containers until I mastered it and here's the trick :o)
Drill a small hole in the top and use a syringe to fill. I used the point of scissors to make the hole.
I used 150 ml of chosen shampoo and topped the rest with water. The containers take 1 litre but I couldn't fill it to capacity as they collapse as they empty in the 'real' refills. I got near enough and it mixed as I filled it so slowly. It works and feels as cleansing as the ready made real refills :o)