I'll give it a try. First, since this is for a science fair, I will assume your gasifier will be small - table top size - and that it will not actually be operated during the fair. BTW, I have judged several science fairs and the most successful projects are those that are a solid demonstration...
Howdy,
This is out of my field but a simple solution might be to install a small check valve open to atmoshphere on the high point of the discharge line. When the pump is off, the portion of the line downstream of the check valve would drain but the seven-foot head would be maintained (the pump...