I have recently found that the Hayes tanks have been taken over by MECOA.com   The 3 oz tanks have been a favorite of mine and others  for many years. The attached picture is of the setup I use on sport planes with the molded in vent set to the outside. In this configuration the vent functions as a uniflow vent  and there is very little mixture change throughout the  run.   Fueling is a bit tricky as the model has to be pointed down to fuel, and let the tank vent air through the needle valve .

Even though I'm pretty much exclusively building full-fuselage planes these days -- woo hoo!

I like your uniflow idea.  You could take it a step further by drilling that nipple out to 1/16" and putting in a length of 1/16" brass tubing (K&S makes it, although you'll probably need to get it from Amazon).  That would put the uniflow outlet at the back of the tank, where it belongs.

With most plastics if you drill a hole with a size X drill the plastic will flex, and the result will be just enough undersized that a size X music wire or tube will be just the right fit to put the tube in by hand and have it stay forever without leaking.

Yes the Hayes tanks are on the MECOA website, click on the Hayes logo. When they set up the FP20 with this tank the mount it with the foot to the bottom so the tank is narrow and tall. They plumb it with conventional clunk and vent (non uniflow style). I have tried it the way you have it shown, I drilled out the top vent and fished in a 1/16" piece of tubing to be the uniflow. It worked but not the greatest.

Best,   DennisT

I put them with the foot down and close off the middle nipple after filling.  The nipples are pointed forward. Works fine for me on profiles.

I have a question.  What does cant mean and how is it done?

Thanks for the reply about the cant.  I think I will try it.  Thanks again.