I made one, very simple and very cheap.
It works by holding water in the tube when you close it after refilling from the same hose.
Drew this up of mine. The ball valve should be below the base of the tank so there will be enough water in the pipe to pull water out next time it's opened.
If you want the intake to be very deep in the tank, the ball valve will need to be even lower, at least 8in.
I have mine half way in so it will drain by itself for a 50% water change. My hose is the right diameter that I can put it into my kitchen faucet to refill.