Proptop

A bubbless tank uses no clunk instead just has one tube going into the bladder through the neck of the hardcase. The end of the tube goes to the middle of the tank and has a short piece of fuel line on the end to pad the bladder when it collapse's on the end of the tube. Also there is no need to pad the tank, it cannot foam.

One of the disadvantages is its delicate and in any kind of crash the bladder will usually rupture on the pickup tube. In the case of the tetra, the outer case is identical to an ordinary case except there is a nipple in a forward lower corner (this is for the exhaust line), the feed line goes through the cap which is goes over the tank neck instead of a plug type normally used and has a hose clamp around it. The bladder itself is just stuffed through the neck, the end of the bag is turned inside out on the tank neck, the cap goes over this and is clamped. I have not tried making a tank but have successfully replaced original bladders with baby bottle liners in the Tetra hardshell (too many midairs).

Pylon racers usually fuel with a tanker (big syringe) which pulls all the air out collapsing the bladder then pushes fuel in after which the line is clipped off with forceps untill flying. There is another method involving a fill line also going into the bladder to allow the use of an ordinary fuel pump and the info for this setup is spelled out in the tank instructions. I think this is the method used by some of the pattern folks with larger tanks.

Djlyon
I recall a couple of years ago at the London Bridge float fly a Balsa Nova finished in very similar colors to the one in your avitar. Was that perhaps you?