cool. thanks mate. im off to go see what a float valve is lol. ive got a 20L NFT gro tank that ill be adding an 80L top up res to. thought i could maybe just run a hose from a-b and connect it at the bottom of the tanks. my theory being that the 20L res would have enough pressure to keep it from overflowing. glad i asked now lol. illgo have a peek about then get back to you. cheers again bud : )