Let's go thru one thing at a time.
1. Should not have to point nose down to drain, nose up if anything to get last drop but level should be good enough.
The fuel lie that feed fuel to the engine should be attached to a flexible line in the tank. The flex lin should extend toward the rear and have a weighted pickup on it. The end of the pickup should come approx 1/8 to 1/4 shy of the back of the tank, definately not in contact. The purpose of the weight is to stay at the bottom of the tank in whatever attitude the plane is in and maintain continuous fuel draw. If fuel draw is being interrupted prior to near empty tank, something is wrong. Even a very small pinhole in the pickup line will allow air into the line and kill the engine
2. The tongue suck test- Haven't heard quite that before but basicly it is this. Squeeze the vent line tightly shut and suck on the carb line. Jaka then wants you to put your tongue over the end of the line and see if the unit maintains vacuum. I prefer to cap the vent and place tank underwater and blow into carb line and look for bubbles. Looking for tank leaks here. Neither of these will spot an internal leak though.
3. Tank and prop you have are fine as long as they are in good condition.
4. 10% is good
5. Glow plug is good type.
6. May need to adjust idle mixture at later date, not a concern just yet.
7.With the engine tuned "just off peak" like you have been, by raising the nose you are making sure that the change in attitude and relative position between tank and needlevalve is not going to over-lean the engine. If there is no loss of power all is fine. This is done at full power.

Next?

Jaka, if I guessed wrong at your technique, please correct me