[A/S] Leaking water tank

[AirstrmCamper@xxxxxxx]

Help!

I just discovered that my 79 31' center bath Sovereign's fresh water tank 
leaks. I never until this past weekend filled it with water. I had just put 
some in to test and get the water pump fixed. Well saturday I filled it, all 
50 gallons worth. When I finished and camne around to the curb side I heard 
the sound of water running. The street is rather slanted so the water was 
coming out of the cover pan by the axle at the curb. It continued to leak 
till the water level in the tank reached about the half way mark and then it 
stoped. If I fill it any more it leaks. When I looked inside at the tank, at 
least the part I could see, there is some sepage about halfway up at one of 
the points where the water level sensers go, but not near enough flow to 
account for the flow that comes out.
The questions are where could the leak be?is there maybe at the halfway point 
a line or valve? How hard is it to remove the water tank?Can they still be 
bought for a 79 Airstream? and if so how much? Can the tank possible be fixed 
if it is craked or should I just get a new one since this one is 21 years 
old. I want to get one like the one that is in it. Kinda like the solid stae 
panel and being able to check the water level.
Thanks.
Jon