RE: Filling the tank with the cowl on
Fueling valves are notoriously unreliable and have witnessed many folks experiance much frustration and lost flying days trying to figure out what is wrong. Many also require a special fitting on your pump line.
Three line systems with or without a second clunk work OK but still offer up lost flying time in if that tiny plug is lost (a common occurence). In addition a second clunk if used reduces your fuel capacity.
Filling through the feed line with a simple plugged T is dangerous to your engines health especially if you have a 135 degree or inverted engine due to hydralic lock.
The most reliable method is always the KISS method, a simple two line system exactly as used on a trainer. Its very simple on a fully cowled engine. The feed line is run external at the front of the fuselage or just out of the cowl and then right back in with a small amount of slack. This allows the flush little loop to be pulled out a little and at this point the line is cut and a short tube is inserted. If you desire the same can be done with the pressure line which will of course give you your full tank indication as usual.
The procedure is to pull the little loop out and separate at the break and same at the vent line if needed then fill just like a trainer, simple. The replug both lines and your done, hydralic lock is not possible. On my inverted cowled installations or 135 degree mounts I don,t bother with the vent. the drip at the muffler is almost as instantanious as an open vent line and due to the muffler being at the bottom no fuel can reach the combustion camber to cause hydralic lock. You can see this setup in this picture, the right engine has the feed line neatly tucked in and the feed line of the left engine is pulled out where it can be separated for fueling.
John