In general, the tank should sit on padding and be held by rubber bands to help isolate from vibration.
22,000 with a 6 x 3 sounds almost impossible.
Make sure the prop and prop bolt are running nice and smooth with no vibration.
You can hold a running model in your hand and cancel out fuel foaming, but shortly after release the foaming begins. I'm not saying this is your problem, but it's something to keep in the back of your head.
I agree that Sullivan brand small tubing is the best stuff.
A handy tool for fueling and trouble shooting fuel plumbing issues is a Monoject 2 oz syringe with a short hunk of 3/32" brass tubing pressed into the tip. You can use the syringe to pressure check the plumbing and to suck out any possible clogs.
I would also entertain the idea of buying a couple 6 x 2 props from APC, or maybe a 5 x 3 rubber prop from Cox International instead of using 6 x 3s. The lower load props are easier on the engine, making tuning less critical. The 6 x 2 might give you the laps times that are slow enough to enjoy but still plenty of inertia to maintain line tension. It depends on the model's weight and wing loading. Experimenting with different props can be dangerous if adequate line tension is lost, so always be cautious.