pipe=cylineer, sol volume=pi*radius*radius*leng
=3.14159*.5*.5*leng or 0.7853982162*leng
but need tu konvert gallons tu sumthun bout inch
1 gallon=230.995130923 kubik inch
yu ask for 0.375 gallons...85.468198 kubik inch
so leng=85.468198/0.7853982162
=108.821 inches
or 9.0685 ft